Tell me about it. I've "lost" several hundred dollars by buying games which later on had deeper discounts, and I still haven't had time to play 99% of them. It is somewhat painful to see a game on sale for $5 when I paid $20 for it (which was a good discounted price when I bought it), but my mindset is the same as yours -- I have the game in my library, so I can play it whenever I want. It costs more doing it that way, but I have several games in my library that have since been delisted from the store. I also look at it from the viewpoint that when I purchased the games, I made the conscious decision that they were worth the price I paid, and a deeper sale later on doesn't change that.

Regarding the offline installers, I have so far always downloaded the offline installer when I purchased a game, but like you said, with games becoming so large (many games being 50+ GB now), that will probably stop. It's also questionable if always downloading offline installers is useful because if you want to have the latest version available for (re)install, then you'll have to download new offline installers whenever a new version of the game is released. If you own only a few games, that's easy to do. If you own several hundred games, or very large games, then it because prohibitive time-wise and bandwidth-wise.