My two cents - we are seeing a market uptick that is in no way related to 41p.
The MG market was really soft in 08, and growing by 2010, and I think it's been really growing since then. 41p (IMO) hasn't made a significant dent in driving MG prices. I believe that MG prices are being more moved by some segments of the economy and still a bit by folks learning that MGs are legal.
While there is a small supply, there is a large demand and a lot of that is in a series of very small niche markets. For example, if someone wants an MG81Z, the options are to pay for a good example or grow old and die. There is no option to maybe wait for a bargain to come along. OP mentions a RLL, of which 538 were made and who knows how many are still on valid paper. At any point, if you dug really hard, you'd find 1 or two for sale. Not much power for a buyer in that case.
Sure there are folks who want to just simply "get" any MG. That's the factor that has pushed up the lower end of the MG market (specifically, MACs). That said, MACs are a good platform that is very interchangeable. That also helps value, a shooter can get more use/configurations/fun out of his single registered MG. This, and the blooming aftermarket, has driven 'modular' type MGs up in price. MACs, AR/M16 platform, DIAS, RLL, HK sears & triggers. But nobody is going to want to get a first, cheap, MG and sign the form 4 to take possession of a Chauchat...
And realize anything in the registry is almost 30 years old at a minimum - and there are a lot of things represented that just aren't being made anymore - things that are still cool as can be. Thompsons, BARs, MG08s, etc. These really are collector type guns. Sure they get used, maybe, but the very nature of being old and out of production and iconic drives collectors who want that particular model. And if you are paying $20k for an MG08, it makes sense to pay $25k for the one you really want and not the first one you see. This is a very different market segment, and it does take money to play here. Part of this is driven by the one-way escalation of scarcity, and the other portion is that money isn't that tough to come by. If you were in a coma, you could have gained 15-20% in the market this year. Diverting a little bit of that profit to a fun item isn't very tough to do. If you are calculating mag dumps versus cases of ramen, this isn't your MG purchasing strategy.
What I have seen personally (I am an 07/02) is 41P is driving a lot of folks who do not own NFA to go for SBRs and silencers. Haven't seen anyone firsthand jump into a MG. Have had a lot of people ask, but what's a good entry MG to recommend ? A MAC and folks who aren't insane dont want to drop 5k and wait a year on an ugly sheetmetal box (no offense to MAC owners!). 99% out of the time, the question then goes to "well how much for an M16" and then we start around $15k.... And this is pretty much beyond the realm of reality for anyone walking into the neighborhood shop.
Personally, I bought my first MG - a RLL - in 2008. It's been a great entry point because you really can get a lot of flexibility out of it. Hosts are pretty easy (even if you $200/SBR short hosts). I still stand by the RLL or RDIAS or HK sear/pack as the best bang for your buck and you can virtually have half a dozen MGs for one stamp.
And I am comfortable enough with the MG market that so far in 2014, I've picked up two more MGs for my personal collection.