My experience has been a little different. Like you, OP, modularity is very high on my list. But I started with a Colt M16. Why, because I wanted 5.56X45, 7.62X39, 6.5 Grendel, 9mm, and .22lr. But I wanted more and the MGI modular magwell system promised more. So I sold the Colt and bought a DIAS. I bought a HK sear because my brother was running a sear in a converted 94 and the only function problems he had were of his own making. So a bought a Vollmer converted 94 that was married to the sear. At the time I had no intention to do more with the sear than that.
This was in the 2007 time frame. I have around $20,000 in the DIAS and HK sear. I have somewhere around double that in firearms for both sears. Now I am getting into Mac style RRs. I am so glad that I got the big money guns first. Today's market price for those two sears would be in the $65,000-$70,000 price range. I would not own both right now. Yes, I would agree that the Mac style RRs are poised for a rise in market value. Between the CF(W) bolt and the Max-11A/15 prices are already rising.
If you have been around the firearms game for a while you also know that things can turn on a dime. Say both the M11A1 and the HK sear raises 50%. The M11A1 would be somewhere between $10,000 and $11,000. The HK sear would be over $50,000. To me, if you can afford the most expensive on your list, buy that. Even if the M11A1 goes to 200% of current market value, that is still less than the current market value of the HK sear. YMMV.
Scott