If the difference is with the engine, do you actually feel the additional power in the 335?

Is it worth it to pay more for the 335?

Is it worth it to upgrade to the ix (all wheel drive) ?

The 335 is legions beyond the 328. If you like power then YES it's worth the money. The 335 is actually very close in performance times to the previous M3 model which is one of the most amazing cars ever built in it's class/price range.
So if you want $60k + performance at $40k-ish pricing then the 335 is well worth the money over the 328.
If you don't care about the power then don't spend the money.

A friend who's a BMW Mechanic once replied to a question about the benefits o the additonal HP of one engine over another by saying, "If you don't know then you don't need it".

the 335i costs 6,500 more than a 328i.

but the extra 6,500 isnt just for the engine

the 335i comes standard with power front seats with driver memory (the 328i doesnt, and its a $995 option), the 335i comes standard with xenon headlights (the 328i doesnt, and its an $800 option)

the 335i also adds chrome vertical slats in the grill (as opposed to the 328i which has black), the 335i has larger wheels standard, and dual exhaust vs. the 328i single outlet exhaust

BUT...if you get a 328i with power front seats and xenon headlights (which are 1,795 extra) then you would only have to fork over an extra 4,705 for the 335i which already has those options included.

the XI (not IX) is an extra 2,000 and in turn makes the car slower, handle worse (except in the snow), and get worse gas mileage. so i dont think its worth it

but the 335i is definately worth the extra dough (if you can afford it)

HOPE THIS HELPS ; )