I don't think you should necessarily reduce the number. Just remove (literally) unplayable maps. The thing that keeps MTA and more specifically Mr. Green awesome is the infinite amount of content. Many of the 'good' maps is just more of the same. Shitty mappers like myself tend to keep things interesting because it makes racing more diverse and in some cases allows new comers also a chance for top 3 finishes.
Thanks a lot, V4POR.. Thats exactly what I mean. Love to see my name on the list, unfortunately its on the wrong side of the list, but I'm sure there are some (rare) people that do