Yes, i upgraded my stadium, maitenance cost has been doubled indeed, however, if it helps me to win matches i don't really care, because it'll help to improve my team's rating and, in long term, attendance....... i must to be careful to not increase my stadium capacity if not needed, inomes increases too, there's no money lost if i keep my stadium full every match......now, you ask me if it's really worth? Give me a couple of games, if my team start winning i'll gladly say yes
Now, you ask me if it's worth to improve my player's room? Well...... i made a lot of profit buying and selling players, if i don't have enough budget to cover their wages i can't buy those players before..... so i'll say yes, it's worth.