The last thing you should do in DV is 'buy an all-around stud muffin'. We see low division teams do this all the time and it rarely works. For example, you'd be much better off taking $100,000 in weekly salary and giving it to 5 guys at $20,000 salary each then one guy at $80,000 and 4 guys at $5,000. Balance is always more important than having 1 so-called stud.
My #1 piece of advice would for you to be patient. That $$$ isn't going anywhere so you don't have to spend it all today but if you truly think you have a chance to promote, I would first upgrade your arenas and then I would upgrade your team. If there's a monster in your league that you won't be able to beat on the road in the playoffs then wait for the off-season to upgrade your roster.