You go into St Pete's and one of the first things you see is Michelangelo's Pieta. It's beautiful, simply, a physical paen to the love of a mother for a son. It is slightly larger than life. Further up there is a statue of the eponymous saint. It isn't a very good one but it too is slightly larger than life.
All around are other statues of Popes, these are huge, baroque, overbearing. Symbols of human power and arrogance, metal boasts of wealth and patronage. You look at them and see one of the main points of the Reformation.
I recall that Christopher Hitchens once described himself as a Protestant atheist, perhaps for the same reasons as you've outlined.
I've never really thought about it in such terms, but now that you've raised it, I am aware that I find Catholic churches, especially of the traditional type, ugly in a gaudy, showy, we would now say chavvy sense. Too much bling - gold everywhere, gaudily painted plaster statues. To my sensibilities at least this:
http://l7.alamy.com/zooms/448fbb05d87848c3a486b84a064043f1/interior-of-a-catholic-church-bgda8p.jpglooks cluttered, fussy and self-consciously show-offy (never mind everything else you said about it being a willy-waving statement of temporal power and wealth), whereas this:
https://s-media-cache-ak0.pinimg.com/736x/13/02/6b/13026b4ca185c27b8f2d7d86245b0561.jpgseems the opposite - clean lines, pure colours, simple. I feel the same way about Gloucester Cathedral, by far my favourite of the many I've visited so far:
http://www.centralhotelgloucester.co.uk/wp-content/uploads/2013/03/GC1.jpgand not this assault on the eyes:
https://upload.wikimedia.org/wikipedia/en/e/e4/St._Louis_Cathedral_Basilica_Main_Isle.jpgThis is a surprise to me as domestically I'm very far indeed from liking minimalism; it's just that the latter building looks minimal in a good way - if you're supposed to be there to worship God, then God is presumably what you're supposed to be concentrating on, not the gaudy tat up at the far end.