Seeking replastering / renovation advice

Hi,

I've been reading alot on various forums indicating that new plaster nowadays only lasts on average 5-10 years. I find it highly likely that new plaster materials are simply not as durable as was the case years ago - that wouldn't surprise me a bit since it is that way with alot of things. Then there is the whole ultraguard option that I've been reading about.

My pool is 23 years old (15k gallons) and still has the original plaster, but a good portion of the pool is apparently worn down to the gunite. Plus, there is algae growth on all of those rough worn-away pockmarked areas. Over the last few years, I've been doing underwater patching to the larger areas where the cement is exposed, but now it's sort of a losing battle since rough and worn spots are emerging pretty much across the entire bottom.

In thinking about my situation, a few questions present themselves: Is the algae eating into the gunite? Is gunite waterproof? If not, am I doing any damage to the actual shell by not replastering and continuing to erode the plaster finish?

I don't want to jeopardize the pool structure by procrastinating on the idea of replastering, but neither do I want to invest money in a restoration job that might not hold up well. If anyone has any advice as to what the best finishes available are, how much I should expect to spend, etc., I'd appreciate any thoughts.

Thanks.
Keith