I wouldn't consider it an amazing mod community. Skyrim is an amazing mod community, Fallout etc. GTA4 mods are mostly garbage with a few that enhance graphics but also make other parts of the game look like crap.
Fan patches never fixed the optimization issues with GTA4 either, what fixed it was PCs getting 2-3x stronger on average then they where during it's release. On it's release you couldn't even run GTA4 as well as a 360 could. A 360 with 512 mb of ram, 1.3 ghz triple core. Rockstar ports are no thanks to me, until they are 5 bucks years down the road. Total crap on release.