as mentioned the M/L-A versions are an upgrade but the normal W versions are usually quite good also. I had a nice copy of the non-ULD 50 for example, and it was quite good (despite some folks claims to the contrary). the 50ULD is better, though. So I switched. I'd say keep the version you have and enjoy it for a while, and only consider upgrading if you find flaws with the one you have.
I think the 65 L/A is sharper than the 110 for the most part. the 110 does have very nice bokeh though.
i lucked into a near mint 140 M/L-A that had a problem with the floating element, for only $59. About $20 in parts from mamiya, and a DIY repair on a stripped gear, and it's good as new.
I did part with my 180 W-N when I got a 210 and 250 APO, but later reacquired a version of it (the Short barrel version) for use on the TS adapter.
All the APOs are fantastic, really top shelf. I have MTFs posted of them from old mamiya literature at
www.edsawyer.com/lenstests/ - have a look.
The 350 APO is excellent. Make sure to get the support bracket if you can, it's pretty key in the use of that lens. It can be used w/o it but requires manual support of the lens. Kind of unwieldy to handhold that way.
the 37 is excellent, very good across almost the entire frame. There's a tiny bit of lateral color in the extreme corners but that is to be expected. At it's best though, in the center 60% of the frame, it's on par with the ULD 50. It's a fun lens, esp. for use as a walkaround lens. Some fun shots to be had with that.
-Ed