Hate to rain on your parade, but if you are looking to upgrade your spyder, you might be better off buying a second hand electronic marker. There are loads of LCD Angels/Impulses and the like in the classifieds.
If you are using a spyder 'cos that is all your local site will allow, then yes a barrel will help. The best barrel I have seen used on a spyder was a J&J ceramic. Not that expensive, and easy to get on eBay (you will end up importing it). Try clicking this
LINK Plenty of upgrades ready for your ££'s.
Air is always a good upgrade for any marker. It will improve the consistancy over the crono' & stop the valve freezing. One of the few upgrades that you will be able to take with you if you should buy a different marker.
If your fingers are fast enough, an eloctronic hopper would be good. For a spyder, a revy is enough. Second hand in the classifieds they fetch about £20 'ish.