Megafobia was never themed.
Wrong. Megafobia is, quite clearly, themed around sheep. ;)
Besides, Megafobia, and the majority of Oakwood's attractions for that matter, look perfectly fine without theming. Theming a woody, unless done properly, is going to detract from the ride, if anything. Again, with the likes of Treetop Coaster, the surroundings ARE the theme...
Speed, there's surely no denying, sticks out like a sore thumb. It has it's own area, and is painted in a bright "look at me" colour. It's also the parks most well known attraction nowadays, I would argue, and it would be nice to see it with some theming... just so long as it's done properly. A half-arsed effort would leave the ride looking worse than it does now.
Glad to see hear that they're looking into another major ride, which will come in 2014 if they have any sense, in order to avoid competing with SW7. :)