I upgraded from the affordable, then industry standard Trantec to a Sennheiser around 18 months ago. I don't do vocals either

, but I did start doing a residency at a club, where I chose to use my own mic, and I must admit that the difference in Audio quality was amazing.
Don't get me wrong, the Trantec gave me many years of faithful service, but when you spend a little bit more you can notice the difference. At the end of the day, you can only justify it by the usage you do. It would be pointless spending £400 on a mic if you only use it for shouting last orders, however, I was / am doing many functions where going out with a Mic was required on a fairly regular basis so I felt the purchase was justified.
VHF / UHF doesn't really affect the Vocal / Mic Quality - that issue comes down to the insert used in the actual pick up of the mic. UHF tends to travel further, and is on a higher frequency spectrum so less likely to "Drop Out" although the use of PLL circuits even on VHF Mics tend to make signal drop outs a rare occurance.
Since the majority of artises / D.J's are still with VHF systems, by using a UHF mic you are less likely to experience intereference to another system on the same frequency if you use your mic in a hotel with more than 1 function room / DJ / Singer

. Most higher priced VHF and nearly all UHF Mics now have the facility to change channel should this occur.
At the end of the Day its your choice - I do recommend the Sennheiser systems - I don't think that I would go back to a Trantec now, however if I was just starting out, or didn't do much Mic work, then I wouldn't spend the £££ required.
Lower priced Audio Technica Mics tend to be very similar to the cheaper Trantec Systems, and I'm not a big fan of their Budget UHF System - which is exactly what it is - BUDGET.
Equally if your current Mic Works, and is reliable then why change?.