Yeah, I think there should only be spawns that are specific to the gangs / characters on that map in single player.
Schark, from what I've seen, there has been a fall in players overall but an increase in GTA3 players. When you say, "Top number of players is 10", I think that applied more to 0.4.1 Portland than 0.5 GTA3 as a whole. To be honest, it was mainly just the Partyserver and I could only ever have fun in the evenings (GMT) when lots of people were on. If I tried playing it during the day, there'd only be 3 or 4 other people.
I think the overall drop in players may be due to the fact that many people have been put off by idiots saying "0.5 sucks" when they actually mean "0.5 VC DM sucks", which puts people off the game as a whole rather than just the VC DM aspect.