I have both (manual 2005 Exi and 2010 VTi Oriel prosmatic) and the 8th gen is miles ahead when it comes to driving pleasure and road handling.
The 7th gen is solidly built and a very reliable car if regularly maintained (I have had it for 16 years now). Parts for both cars is not an issue but 8th gen parts are more expensive.
Fuel average of 7th gen manual is better than the 8th gen manual in city+long route drives. But 8th gen auto gives very good numbers if you drive it on long routes. City driving average is abysmal for 8th gen auto.
The 8th gen interior is futuristic and still looks modern by today's standards. The 7th gen interior is pretty basic but a lot of drivers prefer simple. Passenger comfort at the rear is pretty similar in both cars but front passenger and driver area is more comfortable in 8th gen. 8th gen is not suitable for elders if they ride in the front because getting in and out is a bit of a problem due to lowered height. My parents don't prefer riding in the 8th gen.
Both generations have power steering issues. Headlamp throw in both gens is subpar. Braking performance is equally good even though the 7th gen Exi does not have ABS. No catalytic converter on 7th gen so that's one part you don't have to worry about. AC performance is similar provided you service it regularly.
There are lots of 7th gens in the market with swapped engines. PKDM 7th gens came with D16W9 engine (1.6 L Vti) and D15Y3 (1.5 L Exi). And many sellers don't mention that engines were swapped either because they themselves don't know if the previous owner changed the engine or not or they just magically forget this little detail.
If you have any specific questions then do let me know and I'll try and answer them.
