sorry numanti, but I think you're difficulties are more down to personal inexperience of the D20 system. I've run D20 since the week 3rd ed. D&D came out,and I have no trouble arbitrarily making up stats 'on the fly'.
Equally, you cannot compare the speed you run a game that, by your own admission you have been playing for around 17 years to a game system you don't know as well.
Character gen complex?! You should try Milleniums' End! :lol:
I tried the old GW system and found it a little more complex (I hate random D100 rolls. Especially during char gen. Reminds me of dying during char gen under prime directive and Hol) than D20.
Besides, If your NPC is there to shoot at the PC's, what does he need except DEX score & modifier, Base Attack Bonus, Hit points and a weapon? Reflex and will saves depending on the abilities of the party. Maybe a name if you feel really extravagant?
I think the one thing worth remembering is how familiar you are with a system, the more difficult it is to adapt to another, especially after using the other for a long time. For example, like I said, i've played D20 D&D for a good few years, but I have never been able to truly understand THAC0 from 2nd ed. Even when someone explains it to me intelligibly, I just can't remember it. Why? because I've not used it like they have, even when I've played 2nd ed.
Just my 0.02 creds.