Well, is possible to send rovers to visit other rovers. Has been suggested before. So - could be done. Our rovers can travel for kilometers and you just need to have a landing ellipse that is close enough to the one you want to visit, so that it can hope to get there within a year or two at the typical speed of 100 meters or less a day (future rovers may be faster also).
As for repair - well I suppose depends what it is - if all that is needed is to give the panel a bit of a push to unfold because it got stuck part way - and if everything else is working fine, batteries charged etc - maybe that sort of thing could be done quite easily.
As for a more complex repair such as replacing equipment or mending it - well our rovers for Mars are not built to be modular or easily repaired, and look at how difficult it was to repair the Hubble space telescope.
So - I think that would be far harder to do. Hesitate to say impossible. As to whether it is worth it - maybe it is better to just build a Beagle 3 building on the lessons learnt for Beagle 2? It was a low cost mission in the first place, and so nearly succeeded. It would probably cost a lot less to send a Beagle 3 than to attempt to repair Beagle 2.