I appreciate your message. It looks like you have done your homework very good. You mentioned that your favorite NAIN rug has no signature, but has superior quality and visage compare to the NAIN rugs with Habibian and Aliakaber signatures. It is not really big matter if a rug has HABIAIN signature or not. The real Habibian is hard to find but almost all the local rug dealers have one a Habibian rug. Many of these HABIBIAN signed rugs in the market are faked and the signature had been added to the rug sometimes later.
To show you an exapmle plaese look at the following URL, related to SARIFIAN fake signature. Another famous Iranian master weaver is SERAFIAN in ISFAHAN that are many fake peaces are in the market. You can look at the fake on at:

http://orientalrug.topcities.com/no9942.htm

“Don't buy a rug because of a name. Buy it because you like it”. It seems the NAIN that you like has good LAA number and has a right price. It is a good deal and I suggest buying it. Do not forget to bargain try it for $3800. Negotiate, Negotiate, and Negotiate! It is very common practice in this business!
I am not sure about the SAVEH rug. The only think that I do not like is three colors flag at the bottom of the rug indicate the rug is fairly new. Old SAVEH are very valuable the newer one I am not sure! The price for that SAVEH looks too high. I wish you were able to send us some pictures of your rug. Please feel free to contact me if you have any question or suggestions.