Honestly, Nash is a bit overrated. An offensive wizard, but he was the root of their defensive problems. If they truely wanted to improve their team defense, replacing him was as much of a need as finding a true defensive post presence. Not to mention he was drastically overpaid for his age and shortcomings.
Replacing him with Daniels will help with their defensive problems. Combine that with adding Dampier and they've potentially solved a lot of their defensive problems. They might even be a *gasp* good defensive team.
Adding Harris in the draft and Terry through a trade doesn't make sense in that regard, however (although I approved of both trades, based on what they've given up). Neither of those players play much defense (although Harris has the tools to be effective), and neither have a whole lot of experience being a true pg.
From a team makeup perspective, I actually like Dallas a little better this year. They actually have a center, have capable defensive guards, still have a load of offense, no longer have 8 pf's, of which they'll try to play at both C and SF, and added some youth. Now they're really just lacking a true point guard, of which they hope Harris can develop into.