Moreover, the player that you bought with the spare money is also a potential source of future income, if trained properly.
but i got pretty good trainees, from the money who come out of the arena ;) Maybe it was more intelligent, to buy weaker one because they are all near on top and don't increase value that fast, but i like the flags ;)
I ain't poor after building it(ok maybe 2-3 weeks), but sometimes it was better in my eyes to decide pro Arena and take the succes the next season, instead of burning out.