I have a Zoe Yellow TS Spider as well
The hood problem you mentioned is easily resolved by adjusting the pin that engages with the cover's motorised catch. It just needs a couple of spanners to loosen it off and move it so it engages easily and quickly. Mine was doing what you describe about every third time it was operated. Replacing the rear window is expensive, and needs to be factored into your price negotiation (sounds like you might want to price up the rest of the hood as well).
The other aspects of condition are disappointing but minor - seat wear can be repaired especially if it's black leather, armrest on door is easy to fix back in place - I guess if there are no other body/paint problems, that may be worth doing. There are probably better ones out there, though. Mine has 98,000km (60,000 miles) and I paid the equivalent of £5000 for it in August. Predictably the interior is in perfect condition
Seat height can be adjusted by removing spacers, though the seat has to come apart to do this (not too difficult), I recommend removing the spacers from the back of the rails only, tilts the seat backwards and makes it more supportive under legs.
I'm inclined to agree about the lack of performance. I have a 2.0TS 156 and I feel it performs more eagerly than my 2.0TS Spider - the Spider is quite smooth but generally reluctant to go, especially below 4000RPM. My 156 pulls smoothly through the whole rev range. My Spider had a replacement airflow meter (for the previous owner) to improve its 'flat' performance. For something that looks like a sports car, it's only adequate power... about like having a 1.6 in a 156, I reckon. I have also driven a 1.6 MX5 and while not powerful, it does feel a bit more willing. Lots of cars are faster - my old 164, for example.
I think if performance is a concern you need to stick with your search for a V6 model, but do be careful of the price (over here, they are nearly twice as much) and the fuel consumption (again, twice as much). Even in NZ, the insurance costs more.
You also need to test-drive a V6 Spider or three (I've driven four) because the steering and handling is different again to the TS. I was surprised by how lairy they can be when the body flex combines with the engine's torque.
I'm currently interested in buying a V6 GTV. It is half the price that my Spider was, and while not quite the same condition-wise, it does have the performance. I'm even considering doing a wholesale swap of mechanicals to turn my Spider into a V6. But at the same time, I think the general consensus is that the bigger engine suits the GTV better than the Spider. 'EVO' magazine ran a review of the last (phase 3) Spider and GTV which I thought was quite telling - they found that the GTV was the driver's car, and the Spider with softened suspension and compromised bodyshell was really just for enjoying a cruise.