Originally Answered: What are the disadvantages of a 60 month lease vs. a shorter term lease if the lease terms are otherwise good?
Only one of the factors you mention (high residual) is considered "attractive" in the finance world. "No money down, high mileage allowance, and low money factor" are all suicide terms to a lessee.
Sounds like you got drawn-in by doing what you could to get the lowest payment possible. This tells me one thing... you shouldn't be leasing. You're looking at everything that possibly makes it attractive to a budget, instead of looking at why leasing is a viable option for those who should want it. 60-month leases are almost unheard of, and although the F&I manager might tell you that "this is common in the luxury car world", it's not true. They are used for people like yourself... folks who cannot afford the car otherwise. You're a "payment buyer", and will accept any terms thrown at you as long as the payment you can afford is met. In the F&I world, you're an easy target. Not trying to be rude or lecture, but that's how it is.
In the leasing world, lower payments actually harms you more than helps you monthly. You're only touching the principal amount on a lease as it is, and taking 5 years to get to the residual value is never a good idea. You'll be stuck in this car 'til you fulfill the term, there will be no trading or selling as you'll be way upside-down for the length of that lease. Long-term leases are good for businesses and lessees who are usually given stipends to cover the payments. Leases should never be used to "meet a payment".
Before you unwisely accept a 5-year lease on a vehicle just because of the nameplate on the hood, you REALLY need to look at all factors. Insurance will be higher (you'll need full coverage and then some), you'll really need to watch your mileage limits (no matter the allowance), and wear-and-tear fees on a car driven for 5 years are more likely.
I never allowed anyone to quote a lease out for that far, even on $80-90K vehicles. I even discouraged it for 48 months. The absolute longest I would tell folks to lease is 3 years.
As a rule of thumb, I would say this: "If the financed payment on a 48-month loan is too much for you, then you're looking at too much car."
**EDIT -- Wow, sorry, since you made statements like "I can lower the monthly payment by leasing longer" (twice, actually), it sounded to me like you were having to be conscious of the monthly outlay. Guess I was wrong. I only went by what I read.
As far as disadvantages of a longer lease term, I thought I mentioned those:
"taking 5 years to get to the residual value is never a good idea. You'll be stuck in this car 'til you fulfill the term, there will be no trading or selling as you'll be way upside-down for the length of that lease"
"Insurance will be higher (you'll need full coverage and then some), you'll really need to watch your mileage limits (no matter the allowance), and wear-and-tear fees on a car driven for 5 years are more likely." (Although this is more generic, all are more pronounced on longer leases)
If you want to take 5 years to come to the same conclusion that you would in 3 (you give the car back and own nothing), that's your prerogative. I also question an F&I manager that would want to throw out a higher mileage limit on a long lease, when that person would know it would harm the residual on the vehicle (no matter what it is). That's a red flag right there. And adding miles to the limit would raise the monthly outlay, not lower it. This all smells fishy.
Also, I'm with Satanic on this... I've never heard of a "lease-only" vehicle. Please enlighten me. I've been around the business for almost 15 years, and never have I heard of a "lease-only" car, even Italian exotics.