Independent MPs are brilliant if they have excellent local knowledge, have expertise in some important field (like Dr Richard Taylor), and are fighting on a very specific range of local issues - in his case, saving Kidderminster hospital from closure.
They are not much use if they are like Martin Bell - all good intentions but with no plan once he got there. I gather he got absolutely nothing done for his local area when he was an MP, and had pretty much zero impact on legislation either.
The worst type of independent or minor party MP is exemplified by George Galloway. He does almost no constituency work, doesn't bother turning up to Parliament much, and uses his position solely as a bully pulpit for his ego.
The sector expertise is important when it comes to choosing independent MPs, I think. I would welcome an expert scientist independent MP over a think-tank/intern type who hasn't ever done anything other than politics of ANY party.
All MPs of all parties have the ability to be effective champions for their constituency. Obviously, it is easiest for those currently in government, because pork-barrel projects can be directed to those constituencies.
The trouble with independent MPs comes with the issue of their influence over legislation. Legislating is their main job, really, and this is where expertise can be useful. They won't ever be the deciding vote, really, unless there is a very hung Parliament. Any influence they have must therefore be indirect - persuading other MPs. And MPs of all parties will definitely listen to arguments put forward by independent experts.
These expert-type independents also tend to do a really good job on Select Committees.
So independent is definitely not necessarily a wasted vote - but do be careful!