Our attack shouldn't need more players. I think we are/will be fine there next season.
Depth is always good. Assuming we have two deeper mids again (Pirlo and [Jacobson's Replacement]) that leaves four spots for the attack.
Our currently rostered options should be Villa, Lampard, Poku, Mix, Mullins, Shelton, and McNamara. Lampard can be penciled in to miss a few games due to injury, and will likely often require a substitution at 60' again. So let's say Lampard and Poku are in a timeshare at CAM.
Mix is likely to miss a handful of games due to national team duty again. Also, while Pirlo is out for 5 weeks playing in the Euros, Mix could be needed to slide deeper into his spot.
Finally, you have Mullins, Shelton, and McNamara who have shown some good play, but are not so good that they're irreplaceable in the lineup.
I think at the very least, another striker is brought in. The player Nemec was supposed to be. If we go into next year with just Villa and Mullins up front, that seems like asking for trouble again.
Secondly, if you can grab a high upside young player like Boakai, you probably should. Mix and McNamara are a bit out of position on the wings. Shelton has shown promise, but is far from great yet. Boakai would be excellent competition and could be molded to play in a number of spots up front.