Look for the oval type of pod filter if you must have them. You need as much surface area as you can or they can get restrictive.
If you are selling, I would just give a good clean and make sure every thing works
It will probably be faster with the airbox than without. If you lose the airbox, you still have to deal with the breather and tidy up the area where the airbox used to be.
10 years down the line your bike will be bought by someone who will bitch and moan about the 'previous owner' converting it to a Cafe Racer whilst they convert it back to standard!
I'm not saying don't do it, just don't bother if your going to sell it.