I did much the same years ago. Sold a very nice (and fast!) TVR Griffith 400 (the one with Mk 1 Cortina rear lights and a 4.7L HiPo Ford V8...) for around £4500 to a "dealer" who wanted it for his personal collection. He advertised it not long after for £25000 . Hate to think what it would go for now (I often wonder where it is - DVLA web site says it hasn't been taxed since 1992 and there is no MoT history. Probably gone abroad or been wrecked).
Wanted to reply earlier but just over the shock of £25k for a Senna... I've seen nice low mileage examples struggling at £12k Surely an early 916 Strada is rarer than a Senna and in a nicer colour.
Probably laid up in an old dusty barn out in the country somewhere- owned by some old boy with dreams of getting it back on the road in its former glory?
And most of us (if we are honest about it?) have at one time stored an old project away in a garage or under a greasy tarp? Fully intending to one day start the project - but work,life,wife,kids etc and all the other things that come along seem to take priority and your baby is always the first thing to be put on hold? Mine was a Ford Anglia - the sixties model with the little fins on the rear wings.I got as far as locating a Twin Cam engine,corsair gearbox and differential etc but alas that's as far as I got!