Let's take the basic (we don't know the small print) details of 325.00 a month deal (no deposit)
325.00 x 36 = 11,700
So, after three years, you've spent 11,700 and then have nothing. You just start the process over again and get a new vehicle, providing there's no mandatory balloon payment at the end.
That's probably for 10K miles a year, but we can't be certain.
The alternative is to get a loan for a new car (over a longer term to keep the repayments down), buy a nearly new car, and keep that for 3 years.
If the car depreciates LESS than 11,700, then you trade it in, pay off the remainder of the loan and whatever is left is your profit - repeat and rinse (just the same as leasing).
If the car depreciates MORE than 11,700, then the lease deal would have been better, but the lease company have based their figures on being sure the car won't depreciate that much, otherwise they lose money.
The key thing in your mind is not that you're paying 20 or 30K for car, but how much you will get for it when you sell (the depreciation).
This is why you can buy a nice Insignia for (say) 20K and feel you're getting a lovely car for a good price, then 3 years later it's worth 5K and you've lost 15K in value.
You buy an Audi or BMW at 30K and feel it's expensive, but then sell it 3 years down the line for 20K and you've only lost 10K
Of course, I'm over-simplifying it because there are other running costs to consider and some top brands tend to overcharge for servicing etc (but you don't HAVE to use a main dealer to service the car). Even with those costs.
It's wrong to think '30K' is too much and '20K' is a nicer price. The real cost of the car lies in the actual cost you pay over the lifetime of that car, and not the purchase price.