The other thing to realize here is that the RSD program will basically be the same setup as RLM in that it will use the same site structures, the program will function very similar as it will be a more indepth setup of RLM from what we're told.
This means that you don't have to "correct" things in it from RLM, you extend it further instead. So if you use RLM now to get used to the way it works and such, then open those files in RSD you can finish the design in there without worrying about it messing anything up. They will work pretty much the same so you'll already have an idea of how it all functions when RSD does come out. That learning curve alone is worth the cost of the program I think.
Just my 10 cents, but I didn't want you thinking it was something that was going to be totally different and risky in working with RLM files in RSD. It won't be at all, in fact it will be the perfect way to finish off your RLM designs.