It's not about how old or beautiful the church building is. The question is: IS IT A DUAL-USE OR SHARED FACILITY?
Is it a building that offers BOTH the Tridentine AND Novus Ordo Masses?
Because there are only two options, and both are a non-starter:
Option 1: The Novus Ordo Mass is valid.
Ok, so due to the widespread abuse of Communion in the Hand, you have Sacred Particles all over the floor. So unless the *cleaning crew* has been in the chapel before your Tridentine Mass, then these Latin Mass Indulterers are literally treading on Our Lord during their beautiful "Latin Mass".
Option 2: The Novus Ordo Mass is invalid.
Ok, so heaven help you if the priest distributes Novus Ordo cookies "consecrated" at a previous "mass" during Communion at your Latin Mass. Oh, and you must make a good show of NOT genuflecting in the church until after the Consecration at your TLM. That's a great way to raise your kids Catholic -- don't genuflect in the Church! As they say, the Faith is a habit of life.
And in either case, you have yourself (and your children) immersed in the Conciliar Milieu -- modern art, statues, architecture, banners, flyers, signage, TABLE RIGHT THERE IN FRONT OF THE ALTAR, you name it. You might think it won't affect you, but it WILL affect your children.
So you see the conundrum? Shared facilities are a NO-GO for Traditional Catholics. Better a rented facility, but even better yet ANY KIND of permanent facility: basement, living room, spare bedroom, garage, attic, warehouse, small trailer, etc.
THEREFORE I distinguish between the Indult which is offered at a dedicated facility (Institute of Christ the King has many of these, as well as the FSSP), and Indult Masses which are said at shared facilities.