You can install it without a wipe but if you run into any problems later on you will need to wipe before you can get support here.
To be completely honest though I didn't wipe. Dalvik-cache updates itself so that step is pointless, and the rest, well it will just regenerate a new dalvik-cache based on the new framework.
Give it a try and see how it works for you, but like I said, we can't help you if you start having FC or other issues. You will need to wipe then.
With the combination of Android's internal error handling, coupled with the way ThundeROM is packed, there should be no issues.