The only source we need (Or get for that matter) that comes from HTC is the kernel source. The sense ROM itself has source that no one will ever see except for the developers at HTC. This is to make sure they stay competitive, you won't see coca cola releasing their formula anytime soon because if they do there would be 100 different kinds of coke that all taste the same from different vendors and coca cola would probably go out of business as others would probably sell it for less. The concept is the same basically because if HTC releases their code it is more than likely a company wouldn't just paste it right onto a phone but would take out what they like (The lockscreen, the HTC clock widget, etc).
Now as for the kernel, the kernel is currently liscensed as open source, so any company can take it and use it but when they finally release their product they MUST release the kernel source with it. This sometimes gets a little tricky as sometimes they won't release it right away, but for the most part there isn't really anyone who will go after them, so eventually it gets released for most phones but sometimes it can be a hassle. (I.e. It took HTC I think 2 weeks to release the source for the Thunderbolt, which should have been released the day the phone came out).
So now that we know what we have (We also have code from google for the OS (Gingerbread, Froyo) as Google usually releases it (EXCEPTION Honeycomb source code which Google has yet to release)) we should have a better idea of what the dev's are working with. The kernel and the source for the OS is the only thing needed for AOSP because that is what holds the "drivers" for the phone (I.e. Imo's latest sense kernel was somewhat screwed up as it has the FFC (Front facing camera) inverted, and a couple releases ago he broke wifi with one of his kernels).
Now the whole thing with the RIL is (RIL is baked into the ROM) that we obviously don't have the code for it (HTC will not release the sense ROM's code) so what Layerdaddy had to do was basically take what he already knew about the RIL and try to build a working model. Which obviously can take quite a while. You have to take what you think may work flash it onto your phone see if it worked, and if it did well great, if not you need to get logs on why it didn't go back to the drawing board and start over, or just try to fix what you THINK is the problem. Now that we have a working RIL which the source has been released for (It can be found on tehhaxxors site) we can now take basically any open sourced ROM that we want, bake the RIL into it and it SHOULD work. Which now brings me to MIUI. MIUI is closed source so unless they release source we have to basically do the opposite of what layer daddy did. Take the source of the RIL and bake it into ROM having no idea where to put it which is proving to be *almost* impossible. (We have some amazing dev's out there who are currently making great strides on the project).
TL;DR? No, the leaks themselves do nothing, until they finally release GB and release the kernel source, the only people these leaks help is the people who build sense ROM's off of them.