I've used RLMP since the beginning, and have a good feel for it.

Now that I've used RSD with both an imported RLMP website and a new one from scratch, I'm wondering if I'll ever have to use RLMP again.

Am I missing something?

It really depends on your needs. I look at RLM as strictly a frame work builder and I will be using it for that on one of my sites that's already responsive. I have some features to add to the site that need some fine tuning and more flexibility to get them to work correctly. I have lot of back end support to add and I don't need anything extra making it harder to add it. Altering the existing backbone of that site for those pages would be senseless when I have an app that can get it done in one 1000ths of the time of hand coding it.
RSD simply rocks and I think it will fit the needs for most VSD users. I think there may be a few that don't ever use RLM again but I think most VSD users held out for the public release of RSD and bypassed RLM.