I agree its a crying shamethat there is no aircraft carrier in the UK as a museum, however, having seen the state of the USS Intrepid pre restoration, and seen how much it cost to fix her, I cant imagine any UK company being in the same position.
The problem that running Vince as a museum ship would have is that what do you open - is it the flight deck, hangar, bridge, ops room, accommodation and maybe the engine rooms? (Pretty much what Intrepid has open) The rest of her is just a maze of compartments which aren't really any use to the museum trust. You'd also need an aircaft collection to demonstrate the link to the aviation past. This all equals serious money to keep H&S compliant, maintain the aircraft and also keep the ship in a basic condition where she can be visited safely.
The problem is that I don't see this making much money - there will be a spike of interest, and a steady trickle of visitors, but I don't see many people really making a major detour to see her if she's moored in some out of the way place, and unless she's free, then repeat visits are unlikely.
To be honest, I'd rather see the cash that would go on Invincible spent on the Fleet Air Arm museum, which has an excellent carrier mock up already and which is more likely to survive for the long term.