Frankly, the Shure V15VxMR is the cartridge I would have recommended to you. It is an excellent cartridge that does not get nearly the "rating" that it deserves. It works without a hitch in nearly any tonearm, it tracks phenomenally well, handles warped records better than 99% of the cartridges on the market (due to its' damper brush assembly), has a very neutral tonal balance, and is one of the least "tweaky" cartridges you can own. At its discounted price, it is also one hell of a value.
Unless you need to scratch the audiophile itch, I'd suggest staying with your Shure. On the other hand, if you simply need some adventure and want to try something different, there are several cartridges you could try. A starting point might be one of the mid-price Grados, such as the Sonata, or the Reference (used). The one problem that some people encounter pairing the Grado cartridges with Rega turntables is their tendency to pick up magnetic hum from the Rega's motor. This may or may not be bothersome to you.
Unless you need to scratch the audiophile itch, I'd suggest staying with your Shure. On the other hand, if you simply need some adventure and want to try something different, there are several cartridges you could try. A starting point might be one of the mid-price Grados, such as the Sonata, or the Reference (used). The one problem that some people encounter pairing the Grado cartridges with Rega turntables is their tendency to pick up magnetic hum from the Rega's motor. This may or may not be bothersome to you.