Hard to imagine a potential spouse who would agree with...  "Nah, tell them nothing! Let them guess!"

Yes and no.  Sins once confessed are forgiven but at the same time sin has consequences that can affect relationships ... just as Baptism remits the actual sin but not the consequences of sin.

There are many longer-term consequences of sɛҳuąƖ sin and I believe that spouses have a right to know.  In getting married, the spouse should have exclusive lifelong access to this kind of intimacy and that includes pre-marriage.  So the spouse is being unjustly denied something to which he or she should have had a right.

Those with pasts try to lean on absolution forgiving sins.  Yes, that’s true.  But you forget about the temporal effects of sin.  So, for instance, a virgin has every right to know whether a prospective spouse used to sleep with 10 different people a week.  That would affect the person’s attitudes towards them, could make them more likely to be unfaithful, and there could even be STDs involved.

You should have thought about these consequences before fornicating.  Nice try though.

For example virginity, how many partners, whether one was abused or not, etc?

Pamphleteer Fr. Daniel Lord, SJ said that the answer is NO, assuming that the sin had been confessed and it was not being committed anymore.

I myself have a sinful past and I wouldn't want a potential spouse to know about it.

Would you rather your spouse found out about it some other way?  See my signature.  I think it prudent to be open and honest with a potential spouse.

" whether one was abused or not,"

This can also have huge ramifications, so yes, a potential spouse would have a right to know this as well. 

Absolutely if one is not a virgin that should be told before the wedding.  Also if someone has viewed pornography intentionally even ONE time it should be disclosed.  Why?  Because pornography use by men has the similar effect against pair-bonding that pre-marital sex has on women.  We have been told by our priests that one use of porn can destroy a man's natural attraction for real women for life.  Every woman has a right to know if her potential spouse is a habitual self-abuser.  That will ruin a marriage.  Sex addiction (I don't really believe it's an addiction but I use that term because it's well understood) is not to be dismissed or tolerated.

I think people are using the word 'right' in a more colloquial sense. In the strict sense of the word-- as something to which one is entitled by virtue of the natural or supernatural law-- I find it very difficult to assert that someone is entitled to know the sɛҳuąƖ history of a non-spouse.  I think what people are more saying is that whether or not a spouse is a virgin or a chronic masturbator is going to factor into their evaluation of the spouse's fitness, and hence, is something they would like to know and have reason to know.  And yet, I think in most cases it would not really be a right to know.
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Rights and duties correspond, so if one person has a proper right to a certain piece of information it means another has a proper duty to provide it.  Is it the case that fornicators and the like, especially when they are repentant, are duty bound to disclose their past to others?  At what point?  Is it first date kind of stuff? Engagement kind of stuff?  At what point has the fornicator morally sinned in failing to disclose?  This seems like Scarlet letter type stuff. 
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Here's where it could become a right.  Suppose a virgin suitor says they would never marry a non-virgin. At that point, their consent to marry enters into the picture, and the non-virgin suitor would seem to indeed have a proper duty to disclose, probably out of charity and to prevent them from consenting to something that they would not otherwise consent to.
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All that said, it seems that in general, prudence suggests disclosing for a few reasons, even if there is no proper duty/right to give or receive the disclosure. There is a good chance such information will be revealed later anyways: social media being what it is, people's histories being shamelessly advertised, etc., suggest that a non-virgin spouse will eventually be found out.  Better to disclose it at some point in the courtship than for it to come out later, and possibly risk the other spouse feeling betrayed.  For men disclosing pornography use to their girlfriend's, same idea. Especially if the use has been 'addictive', because it is unlikely, in a digital world, that such a secret will be able to be maintained forever.  None of this constitutes a duty/right, I do not think, but something can be the best thing to do without there actually being a duty to do it.
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It being a question of prudence (i.e., good moral/situational judgment), there will be cases where it is prudent to not disclose, too.

In at least broad brushstrokes, then yes, I'd say the spouses need to know one another's past sɛҳuąƖ history.  Even if, just for the sake of argument, one does not have a "right", still, it's a "better to know" scenario.  And someone having "slipped" once or twice is a whole different critter from having been a whore or a whoremonger.  (I use those terms in the broad sense, not necessarily indicating sex-for-money.)  And the way things are getting nowadays, seems everybody under 30 wants to be the gender and the identity other than what they were born with --- as though people should just be born with an interchangeable set of Lego parts for pudenda virila vel muliebre! --- any gαy exploits, other than perhaps a single drunken incident or two (women nowadays are getting pretty adventurous in that regard, perhaps because many of them hate men so much?), should be disclosed as well.  I'd want to know in either instance.

But let me pose this question --- would substantial error about the sɛҳuąƖ past of a spouse have been grounds for annulment before Vatican II?  I know, nowadays, you can often get an "annulment" just for your jib having been cut differently than what your partner had in mind, but "back in the day"?  If it would have been, can someone supply a source?

And in the interests of full disclosure, Deo gratias, I was a male virgin on my wedding night --- I'd been no simon-pure saint, I'd done things I shouldn't have done (and which have long since been burnt up in the confessional), yes, they involved real-life women, but in the strict technical sense, I was a virgin.  I shall not speak one way or the other about my wife, we are divorced (she lives in mortal sin with an illicit consort) but in the Eyes of God we are husband and wife, and she is the mother of my son.  (Considering the circuмstances, we actually get along quite amicably.)