[AnAmericanMother]

Plus most parishes have junked the old altars, so they'd have to build them all over again.

Nah, all you need is a couple of floor jacks and some spackle. Just roll the altar back to the east wall where it belongs!

There's a historical church downtown here (Immaculate Conception) where they still have the original reredos with niches for statues of saints and the Tabernacle. Moving the Tabernacle (which is stuck in a corner over to one side), the altar and a few floor tiles would do it.

Even our parish church, which is of recent construction, could be reworked pretty easily. You could even add an altar rail without much trouble, and rearrange the chairs along the sides. There's even a rudimentary choir already in place (between the two sets of steps). The architect was very consciously looking backwards in the design.

Our Tabernacle would fit nicely in the central niche of the reredos. (It's currently at the head of the aisle on the decani side.)

[Cicero]

You are fortunate. Our church, like most these days, has a wooden table for the altar. The old altar, candlesticks, and the rest were all junked, and the reredos was replaced with plywood rec-room paneling.

I think there were fresco designs on the walls, but they were all painted over with whitewash. Thank God the stained glass windows remain, but that's about the extent of it.

In my last church, while we were attending mass there, there was some talk of junking the stained glass windows and putting in clear glass. Fortunately the decision finally went against doing this, because the windows had been designed by Louis Tiffany, and the pastor was persuaded that they were too historically valuable to junk.