I think there's a lot of merit to the idea of prizes that build on each other, or are mutually supportive in other ways - sponsors willing of course. This could take many forms. One could be a follow-on prize like LunaTrex suggests, where solving the problem for one prize tends to make teams ready for another, possibly more ambitious, prize. A lot of people have suggested a follow-on to the Ansari X PRIZE, where the technical challenge is somewhat more difficult (greater altitude, more payload, etc). Another variant of this approach would be to gear the prize towards the current generation of suborbital RLVs in development rather than a future generation, and make it a prize that encourages development of value-added services to be integrated with these vehicles. These could involve development of remote sensing instruments, atmospheric samplers, engineering test and science experiment racks, smallsat launch from the suborbital vehicle, etc. They would not necessarily have to be large X PRIZE level prizes.

I'm not sure I'd try a similar approach for the GLXP right now. I might be more inclined, if sponsors were available, to add to the GLXP bonus prize suite and runner-up prizes for now, to encourage multiple, diverse GLXP successes.

Another approach, which I think someone at XPF mentioned recently in the XPF blogs, is smaller prizes that tend to be stepping stones towards the big prize. I think this was mentioned in the context of the GLXP, but I've also thought something like that might be nice for the NG Lunar Lander Challenge.

I also wouldn't limit the "mutually supporting" approach to space competitions. A prize that supports multiple X PRIZE Foundation prize areas could be a big win in the sense of allowing the different XPF areas to support each other. The idea mentioned above of a suborbital RLV environment remote sensing or life science microgravity prize could be a good "2 for the price of 1" combination that gets support from 2 distinct interest groups (Exploration and Energy/Environment in XPF category terms). The remote sensing version would be particularly nice in that it could demonstrate to those concerned with the carbon footprint of the suborbital RLVs (and there are a lot of Internet commenters with that concern) that these vehicles are important for environment monitoring. I'm sure there are lots of other ways to allow the prize areas to help each other.

One other virtue that I'd look upon favorably in a new prize idea if I were making such decisions is suitability for the X PRIZE Cup. It's a great bonus if a prize can be demonstrated in some way at that event, since it would help continue and grow the critical mass of interest for the event (which I hope happens this year). I think it's safe to assume the XPC won't be held on the Moon this year, so we won't see GLXP wins at the Cup, but it would be great to see the GLXP teams there showing what they can. I'd even encourage Automotive and Genomics X PRIZE competitors to show up, as well as non-XPF Centennial Challenge teams, student teams in competitions like Cansat and Team America Rocketry, etc. They are all different, but I think each has something in common with the others, and a lot of good things could happen by putting all of that talent together in the same event.