Think, think, think, why do you want a Se7en and how will you use it? There are many reasons for acquiring a Se7en: vintage racing, racing, building a car with your own hands, hot roding a classic design, autocross, driving a sporting throwback to another era, owing a piece of history… The main considerations should be history (vintage eligibility is part of this), grip, weight, power and cost.
Do you remember the old TV ad for the Triumph Spitfire? “You not only get a car and a girl you get a piece of history.” For the history part you probably want a Lotus built car. Unfortunately to my mind; the noble history of Caterham doesn’t seem to excite many people. Both Caterham and Birkin have romantic histories of their own.
If you want a car built by Lotus do your homework to insure that it is as advertised. There are a great many reasons for calling a car that was not built by Lotus a Lotus 7. Some are simple dodges to get around draconian registration laws, others are simple fraud. Check things out with the Historic Lotus Register.
Do you want to slide around every corner? The narrow section tiers of the older cars let you do that at sane speeds. If you want a trick suspension with fat gumball tires look at the newer cars.
The desire for a very light weight pushes you to the original Lotus 7, more modern cars with basic specifications or the new and exotic carbon fiber and titanium wonders.
Want raw power? Maybe a Stalker with a V6 provides the torque you want. Does the wail of a high reving motorcycle engine turn you on? How about paddle shifting? Motorcycle engine Se7ens are a recent invention.
Do you want to keep costs down? Buy a well cared for used car. Is the sky the limit? You can option a new Se7en into 6 figures if you really try.
My problem is after writing this stuff down I want one for track days, one for touring in the primitive manner and a bike engine car for the sound and paddle shifting. Oh woe is me.