Hi jax,
I've spent quite a bit of time in Lagos over the years and,in all honesty,couldn't describe it as wheelchair-friendly.Most of the streets and pavements are narrow and cobbled and most of the restaurants are old buildings which were not custom-built for their present use,though many of them have outside tables which would be readily accessible with a wheelchair.
As for the beaches,although two that I can think of are accessible from pavement level, the sand is very soft and deep and not conducive to pushing a wheelchair I wouldn't have thought.
I don't wish to seem as if I'm trying to put you off Lagos - far from it, it's a lovely resort - just trying to answer your question as truthfully as I can.
When are you planning to go ?If it's any help.I'll be out there for three weeks beginning 11/9 and could take some photos of the beach accesses and e-mail them to you if it will help.

Thanks for the reply Sagres. We don`t have any definate plans at the moment, just weighing up the options. I just fancied somewhere different and my neighbour has just come back from Portugal and was really impressed with Lagos. I don`t really like purpose built resorts. I like a bit of character but unfortunately character usually means not very accessible. Thanks for your help anyway.