Joe, I have some advice. I tried the same thing a little less than a year ago. EDGEER is right, that you may be better off buying a Tornado table (regardless of price), because they are damn worth it, and they have a great resale value; however, I understand being cautious about shelling out hundreds on a table. At the same time, when you attempt to turn your Sprotscraft into a Tornado, you'll spend a lot of money on the players and the handles (I think the men and handles are over $4 each, so that's about $26x4 for the men and $8x4 for handles).
From what I understand, you can put Tornado men and handles on most generic foosball tables. I took a less expensive rout, and bought Carrom brand foosball men and handles. They aren't the same, but they look and feel pretty similar.
As far as the playing surface goes, you don't need to remove the slopes unless you want them removed. The thing I disliked the most about my table once I modified it, was that the table wasn't flat, and that the rods didn't move in the bearings the way they do on a Tornado. The rods seemed to spin on their axes easily and had difficulty moving laterally. This sucked, because the ball would plow through the men if you didn't have your hands on them (which sucks for playing singles).
If you want to replace the playfield, this can be done simply by putting in a 1" or 3/4" MDF board (cut to fit the field), and I think if you bought a sheet of Formica and mounted it to the board, this would simulate the Tornado surface well. The total cost of the playfield would be about $25 for wood and $30 for Formica.
Personally, I wasn't satisfied with the mods I made on my table. It was better than any other non-Tornado I'd played on, but not good enough. An uneven playfield is frustrating. Changing the surface, and then getting the right balls (experimenting with different types of balls is probably a good idea) will make the biggest changes.