Kwaping,
It depends who you ask. The vibrato is fine as long as you like Fender's scooped, buzz-saw style effect. It's a very Link Wray kind of sound. The reverb tank, on the other hand, is something I just can't stand using. You get one knob for intensity, which controls both the depth and volume of the reverb, so it's hard to find a butter zone. It also has a tendency to produce a lot of excess noise, especially if you're pumping relatively high gain through it. You could technically replace the entire tank, but I'm not sure if it's worth it. In my case, I just bought separate vibrato and reverb pedals that I like way more than the built-in effects.
Most of the modding I've seen on the DRRIs have been tube and speaker swapping to get them to sound more like the old '64 DRs, which isn't that hard. The RIs tend to have a cleaner sound when cranked, and not as much personality as older tube amps that really warm the sound when they're being pushed. If you're planning on playing straight to the DRRI and want it to add more luster to your playing, I'd recommend looking into those kinds of mods. For my case, I wanted the cleanest tone possible at the amp so I could fuck with my tone through a pedalboard, so it works out great.
