This is a very nice pair of mics and a good value. Clear and clean. I've used them for overheads, under snare, classical ORTF pair, acoustic guitar, etc.. If you can afford them, the NT55's are more versatile - two capsules, a pad, high pass. Same capsules as the NT5 though, so you are paying for features, not sound. I bought the NT55s and was using them instead of the NT5's, so I sold the NT5's this summer. Sold them for $305 on eBay. So they held about 75% of their purchase price.
Those are the same capsules you get with the NT55. I think that would be a good option for someone who was recording classical where the omni capsule was the most used feature and the hpf and the pad were the least used features of the NT55. Recently I've found that the pad was the feature that I used the most (for under snare). It's three extra features for about $150 per mic. (I'm really not sure if there are any other differences in the circuit. I've always assumed that there weren't.) I guess if you bought a line pad and the extra capsule and filtered in the box you could save a bit. And if you aren't going to use the extra features it's obviously not worth the extra money. But I've used all of the features at one time or another, so I'm glad to have the 55.
This SDC series from Rode (NT4, NT5, NT6, NT55) is seriously good value and highly recommended.
Leaving price aside for the moment, you have to look at your expected usage of a pair of SDCs to get an idea of what characteristics you need. If you expect to use them for miking a drum set or a guitar amplifier, you need the pads. If you find the HVAC in a venue is swamping you with LF energy (it does happen!), you may need the high-pass filter. If you will be miking a classical ensemble or a piano using A-B spacing, you need an omni polar pattern.
The NT5s could fit the last of these by your acquiring the additional omni capsules, but the first two really should be done in the mic body, and that points you at the NT55s.
Now look at price. The $430 is a pretty average price for a pair of new NT5s, and you could proabably do better than that if you shopped around. Add the omni capsules at around $90 each and you are getting towards the cost of NT55s and you don't get the HPF or the pad. I would go shopping specifically for the NT55MP set (two mics in a hard case), and see what offers you get. The Rode 10-year warranty is second-to-none, and in my experience does not depend on where you bought them, as long as it was legal.
Agreed with the others. I bought my NT5's before they made the NT55's available. They sound great - I have a Neumann KM185 and they are just as extended, almost as detailed - and are a terrific value. I really should get the NT55's for the reasons that were explained by Bob & Bos (hey, THERE's a cool name for a pub!), mainly because in Florida HVAC is always on everywhere and LF rumble can be a real pain during choir or ensemble events.