They are basic but extremely durable cameras. I'd be careful spending a lot of money on one and would want some assurances that the meter is still accurate and not jumpy (as they often get, like my dads). There's a ring resistor inside which gets worn or dirty, and can't really be repaired if problematic (Miles Whitehead cleaned mine which made a big difference, but it's not perfect). Of course, the camera still functions without the meter (or batteries), being fully mechanical like the F, F2, FM2 etc.
My advice with Nikkormats would be to get a later one, FT2 or FT3 - they have better viewfinders with more normal split-image, unlike the FTn, and take regular SR44 batteries rather than needing adapters etc. Also have built in hotshoes, and the FT3 is an AI body, which means you can mount AF lenses too. They only cost a fraction more than an FTn too.
Also quite nice is the EL or better still EL2, which are the precursors to the FE series (whereas the FTn, FT2 and FT3 are the precursors to the FM series). I had an EL2 which was in lovely nick and a lovely camera to use but nobody on here wanted it when I sold it as part of the cull, and it went on Ebay for about £50.
To be honest with you though, considering you already have an FM2 and FE2, I'm not sure there's any good reason to get one, other than GAS!