There aren't many upgrades on the market for the terminator, for a good reason - it don't need them.
For my first semi it was a toss up between a Terminator or an Evo
(and the Evo only happened coz I talked my parents into paying for some of it as my 21st B'Day prezzie
)
They're dead easy to work on as well - if there is a problem that takes more than 2 minutes to fix on an inferno, I haven't come across it yet.