I got around this by placing lots that are too large for the venues, placing the venue lot in the center of the oversize lot, then softening the terrain around the edges. Sometimes I have to add a foundation wall on the uphill part of the lot.
I also deleted one of the 40x40 lots downtown, and placed two smaller lots for the salon/tattoo parlor and the firehall.
Additionally, I am not shy about moving families, demolishing houses, and rebuilding homes elsewhere. I always make sure to relocate any sims I displace, and I build a house to replace any I demolish. That way there are always enough houses for my residents.
Another hint is to use the smallest lot size you can when you create a building to save to the library. Then you don't have to be so careful placing lots for your creations.