The need for a long 3 is vastly overstated on this board.
When the main compe ion was Dallas/PHX, we needed hybrid 3/4 that could used in a small ball line-up/match up with Dirk/Amare/etc.
With the Lakers/Hornets/Jazz being bigger threats, the need is more legitimate beef along the front line.
On the wings, we're looking at Manu & Mason (or Finley or Bowen) being on the floor at the end of games as is. Yeah, all things being equal you'd rather have a 6'9 guy at the SF than a 6'6 guy - but for the Spurs purposes, it really doesn't matter that much.
There's only a handful of big wings in the league that can really make you pay for not having a guy like Ariza to match-up with them - and even then Bowen can usually hold his own against most of them.