Glen Turret is worth a visit.

The Vivitar was the first macro lens I've owned and the only other one I've got is a 100mm (Cosina) so unfortunately I've nothing similar to compare it to. It does seem very sharp to me though, it goes to 1:1 without needed and adaptor and, best of all, it was cheap!

I've been playing around with a number of, mostly very cheap, 50mm(ish) primes recently and have some galleries up with example shots from a few of them:

Porst 55mm F1.2 (http://www.pbase.com/niblue/porst_55)
Helios 44-2 58mm F2 (http://www.pbase.com/niblue/helios_442)
CZJ Tessar 50mm F2.8 (http://www.pbase.com/niblue/czj_50mm_f28)
Pentax SMC-A 50mm F1.7 (http://www.pbase.com/niblue/smc_a_50_17)
Vivitar 55mm F2.8 Macro (http://www.pbase.com/niblue/vivitar_55mm_macro)

I've got a few others as well, including the SMC-M 50mm 1.4 and 1.7 and the SMC-FA 50mm F1.7. My experience with these "standard" primes so far is that they're usually sharp even wide open and, due to being at least reasonably fast, easy to focus even on a DSLR.

Both the above images are reasonable quality (although I'm not convinced about the colour cast in the first one) but neither look to be really, really sharp of have any real bite to them - something much easier to get with a faster, sharper prime.

*istDS, Helios 44-2 58mm F2 @F2, ISO200

I also find DOF preview important however I didn't miss it that much on my MZ5 because I mainly used that for snapshot type stuff and the Z1p, which has DOF preview of course, the rest of the time.

I bought my MZ5 before the MZ5n was available however the latter was a very competent & well specified little camera (as was the MZ5 apart from the missing DOF preview).

If you've already got an MZ5n then I'm not sure why you'd want a MZ5 as well.

I'd agree with John - the 3rd picture is the best because it has drama. The first is a nice scene but lacks any real bite. The 2nd has great potential however I think it needs a single in-focus, close poppy as a larger part of the shot plus more saturation in the colours.

Good start though!

They're often available 2nd hand - mine (an APO Super II in good condition) cost me about £60.

I regularily use a 2x TC (a 7-element one) with my 80-200 F2.8 and it works very well apart from introducing a bit of CA. A 2x TC on a cheap consumer spec lens like the 50-200, or even a better lens such as the Sigma 70-300, isn't a good idea however and the results won't be great.

A decent 1.4x you might get away with in those same circumstances however with the 90mm and 400mm primes mentioned and in decent lighting conditions I'd certainly expect the results to be useable.

It's supposed to be a good lens although apparently it can be prone to flare due to the size and shape of the front element.