Whether it's worth it? I'm not sure...it all depends on what you're looking for and basically what sort of person you are.
The walk from the Riveira area took around five minutes, it really was no big deal, we stayed near the beach but walked that same walk all the time to go TO the Riviera section for the pools. The pools are much nicer here.
Basically if you are staying at the Beach area, you have to walk to the decent pools. If you are staying in the Riviera area you have to walk to the beach. The walk is the same length either way and we'd split our time between the beach/pool so we would have done that walk no matter where we stayed.
Saying that, we saw so many people queueing for those golf buggies it was shocking. I'm hardly a fitness fanatic myself, lazy by most standards, but I've never seen anything like the people unwilling to walk 5 minutes!! But they are there if you want them and can be bothered waiting.
The only difference really is that the rooms and pool, and lobby (lol everything then) are nicer in the Riviera area, so I guess it depends how much time you will be spending on the beach, and how bothered you are about the rooms etc. They were all nice enough in the Beach part, but not modern like the ones in the Riviera section.
My advice? Stay in a Hacienda! Half way between both sections so 2.5 mins walk either way, and they were deserted when we went, so you basically have your own pool, sun bathing area, and in some I think hammocks and hot tubs too!
I won't be returning to the Sandos but if I did I would go for a Hacienda.
If I personally had to choose between the Riviera or Beach I'd choose the Riviera as the walking is honestly nothing and it's just a bit nicer looking, but I doubt it would have much impact on the over all stay.