Personally, I think Collection is fantastic as it is, and easily one of the best 2E changes. Yeah, it's got some bonkers combos, but man, bonkers games are fun sometimes, and Collection gets all the fun parts of Goons without the swingy parts of costing $6 and the Militia attack. It is indeed a very strong and often centralizing card, but it does so without being unfair or ignoring the rest of the kingdom, which is exactly what you want in a strong card--you still need draw and trashing and actual good Actions to gain for Collection to really help you.
I'll admit, Collection does compare very favorably to cards like Plunder, Spices, Groundskeeper, and Merchant Guild which I know some folks may not like. My one potential nerf isn't to limit the VP bonus (guys, that's the fun part, don't nerf that) but to actually just make it give $1 instead of $2. You'd still want these for the VP, but you'd then need other sources of $ to support it. You can still go nuts with Horses, but not quite as nuts. Again though, I still like Collection as it is, and am super happy it exists. (Also, the Stampede combo is super rare you guys, and if you're IRL, just uh pick a different card?).