In my analysis of this and the other card like it in the contest, the conclusions I reached were that you need to play 4 in a turn for them to be individually worthwhile at their price tags. I think that's WAY too much. Compare with other collision-dependent cards: Treasure Map, Fool's Gold, arguably Tournament and Baron. Their powers exceed their cost tiers with only a single collision. Admittedly, you absolutely have to take into account their solo powers (Treasure Map is nothing, while Railway Town is still at least a Village), but it will be extremely unusual to be able to reliably chain 4 of these together per turn, especially once you start greening, and even when you do, it's not stupendous until you get to 5 per turn. You'd almost always rather have four unfettered $5 cards (Festival, Bazaar, Market, whatever) that will reliably produce $5-level effects every single time.
My suspicion is that this type of card needs to achieve at least $5 power levels with only two in play per turn and exceed that with more. For example, if the "two or more times" bonus were +$2, then playing two Railway Towns would be equivalent to playing two Bazaars. Even that might not be enough, because wouldn't just having two Bazaars be generally better, as it wouldn't matter if you drew them together? But you could make it work depending on what the bonuses were at the higher levels.