Generally speaking, I agree that a +2 should be no less reliable than the other cars you mention. They are noted for their lack of same.
All period FIATs are made of recycled rust. You can slow it down but not stop it. And in spite of the fact that many were made, you may find parts availability a problem. For example, I couldn’t locate head bolts for my 124 Coupe when the car was only 15 years old. All FIAT twincams MUST have timing belt replacements every 20,000 miles or you’re likely to need a new engine. And the 5-speed gearbox can be quite a handful as well.
On the disagreement side, I believe it is hard to comfortably buy a “good quality” Lotus and get what you thought you bought. This list, for example, is strewn with owners who paid a premium to buy a clean car from a dealer and found themselves with a rat, shoddily restored or “rebuilt” by slapping in rings and a head gasket and lapping the valves. Check the older posts to see what I mean.
If you want a reliable car, I’d look for a well-sorted Zetec that has a good list pedigree, as in the owner is well-known and respected. With few exceptions, buying from a dealer is a good formula for grief as they have no more obligations with older cars to reveal the truth than an owner does. And you can verify if an owner really cared for the car. But these cars are few, and you won’t buy them cheaply.
If you want an original car, I’ll offer that you need to expect the worst from whatever you buy and therefore may be best off with a tired car that clearly needs work. I’m personally in the market for either a Just 2 or +2 and would prefer a nice car cosmetically with tired mechanicals because I like working on mechanicals better than sanding fiberglass and filling my nostrils with paint overspray. Decide what’s best for you, but bear in mind that the pedigree matters. What the owner or dealer say about a car is one thing, what others say about it is something more.
I’ll also offer to beware low-mileage cars. They have most likely spent long periods laid up in garages or fields, and sitting idle is not a good thing. Any original bits that are over 30 years old aren’t new anymore, be honest with yourself!
Better a car that is loved by its owner, kept in running order, and used regularly.
Go with a Lotus, good luck, and have fun! But don’t expect it to be as reliable as a Toyota.