I played SP also almost from the beginning.... My first reaction to SP1 was "gee, 'tis somewhat complicated to me" (I was about 13-14 back then?) but then I've watched my brother playing it and I got hooked...
On SP3 I disliked many things, like that weapon ranges were reduced four times but the movement wasn't, so almost any unit was able to outrun shots... I have made my own mod with speeds halved (originally also reduced by four but then it was too slow) and I have made many other goodies like on-board DD's for WW2 or on-board planes as A-10, Sturmovik or so (I have used internal rules such as that the planes must move at least xx hexes in one turn , but onboard usage allowed to better simulate the deployment of low-level attack planes hiding behind the ridges etc.)...
Overall... SP got a long live and now I am enjoying fully WinMBT and I am waiting for WinSPWW2
)