If those are ETJ/ETW phones, then the display problem is an easy fix. It's really a problem with gravity and people dropping the phone on the desk. The display connector comes loose real easy and just needs plugged back in. If they are DTP/DTU phones, the display is a modular piece that sometimes needs reseated (phone stays together, two screws for display). The DTR/DTH phones have the worst LCD issues, and I haven't taken those apart yet.
Shore-Tel is just..ok. I've seen a lot of buyer's remorse on that one and mostly on the support side. Try to get some input from reviews and forums. My personal opinion is that VoIP is an absolute waste if it's all contained in the same building. I can understand why an IT guy might be interested, but it's only skin deep; it's still telephony, but with a different way of connecting to the switch. The nicest thing about VoIP phones is that you can plug them in anywhere (literally), you can use third-party SIP phones, and you don't have to mess with a cross-connect field. But the nuts-n-bolts of it is that it's still a head-end, copper connectivity, and a phone. You get basically the same thing, but with connection and quality issues on top of telephony issues.
I know that the SV8x00 is a VoIP switch, and I may have just contradicted myself, so I'll point out a couple of things. First, the telephone sets are usually most of the cost. Since the system is hybrid TDM/IP, you can take your time integrating newer phones into the system. Second, NEC is only producing the Univerge and DSX platforms now - an IP hybrid and an over-the-counter. The DSX really doesn't count since anyone can buy it, it's very inexpensive, and it fills the SOHO niche. Sweet little system, though. So a company that's been around for a long time, has a very high market share, and still has systems operating as long as they've been around (I serviced a 616 last month, over 20 years old!), and is now staking it all on a single platform, either has a great product or great support.
However, since you mentioned that you are IP oriented and are looking for an IP switch, I will echo what Ozzie asked. Why not upgrade to an 8300? It can do everything the Shore-Tel can do, including easily swapping phones and moving extensions.