As far as games, I'd need to look and see which ones I like are AGA. There are some AGA games that were very cool. Honestly my primary game platform is Commodore 64, not Amiga (though there's some great Amiga games). You seem to be suggesting having difficulty running AGA games on your AGA machine with WHDLoad... you might want to ask people about that if so. I've had great luck with WHDLoad, though most AGA games run fine without it on my 1200. Unless you have some floppy only AGA game you want to put on your hard drive, why are you even using WHDLoad for AGA games?
When it comes to demos, though, AGA stomps all over anything ECS could even imagine. There's also a bunch of cool graphics apps for AGA which I don't use, but if you're into that sort of thing a non-AGA machine will hold you back a lot.
After having a 1200 for a while, if I had to go back to using an older Amiga without AGA and the other improvements in the 1200 and 4000, I'd probably give up on my Amiga hobby completely.