First, congratulations on making the finals, Pop is a hell of a coach and you have a hell of a TEAM (meant in the best sense of the word). I've been advocating for the Wolves to try to hire Chip Engelland away from you guys to help develop Ricky Rubio.
Second, my thoughts on your team:
1. Considering you've at made the finals this year. The core is untouchable. There is simply no reason to break up a team that's made the finals twice in two years. Let them play out these contracts and ride off into the sunset.
2. Tiago Splitter has an awesome contract (I love declining salaries) but is almost 30. I'd considered offering him for Omer Asik but was saved from myself by moving way too slowly. I don't see any other very good players but I would be open to moving him if it were in return for very good parts that can play now (I can't find anyone that makes sense). Update: I was offered Jonas Valancuinas for Tiago but I turned Toronto down (if anyone is into stats and has watched him much Jonas has one of the largest discrepancies between WS/48 and RAPM/RPM that I've ever seen).
3. If this were more than a mock draft you have some serious cap space which I would use to go after Kyle Lowry with the promise of contending. I respect his defense and off-ball play well enough that I think he can easily get 36mpg playing the 1 & 2 spots alongside Parker and Green respectively. I would then use the MLE (I'm assuming it becomes available, I'm not a salary cap expert) to resign Diaw, worst case you could go after Ed Davis but he doesn't have any of Diaw's ability to space the floor.
4. Kahwi Leonard is really your only potential moving part that could induce a big return. How highly do you value him? I offered him straight up for Kevin Love and unsurprisingly was turned down, I may offer him for Harden but I feel like Harden is Manu 2.0 and right now Kahwi's defense is more valuable, but if you're looking down the road it would make a lot of sense; regardless, there's no way Houston does that so the point is moot. I don't see any other potential trades that would actually help the Spurs. Trading him for a star seems reasonable, trading him for a high draft pick is out of the question as this team needs players ready to contribute now.
5. Pick #30 - I personally am hoping Spencer Dinwiddie falls but I know there are a couple of other guys on CH who love him so I doubt he's available. Here is my personal big board (not a mock, just my subjective rankings) I'll probably just take best player available. These are heavily influenced by Layne Vasho's Expected Win's Produced regression model for college players with subjective placement of international players based on draftexpress' profiles. Layne is a frequent poster to Canis so everyone knows about his model so I rather expect any "value" I get would be international which feels very Spurs-ian.
6. Pick #60 is barely worth discussing but you can argue about the second half of my big board if you have some really strong feelings.
TL;DR; The Spurs are in a great position for one more run, there's really nothing for me to do except take the best guy I can find. At some point you're going to have to get younger but this isn't the time IMO.