Andy,

I would suggest buying a 1.5 year old Tuscan Speed Six Red Rose, which is effectively what the Tuscan S is, without the badge. You should be able to pick one of these up for about £30-£35K & expect it to be worth at least £20K after 5 years, which makes the sums much more attractive
(although I would expect your servicing costs to be a more than than £500 per service, unless you use an independant garage. You should also add £500 a year extended warranty, if you are buying a second hand car)
Also I am surprised at your insurance quote - mine is WAY cheaper than this - try Sunninghill 01276 474844 - obviously I don't know your age, history etc, but that sounds high...
As to tyre wear, they are surprisingly light on them - I've done a couple of track days in mine & 7000 road miles from new, & I've still got plenty of tread on the original tyres (The 7000 miles have all been fun/thrash miles - I don't use it for commuting, as I work from home)
As an empeg & TVR Chimaera owner myself I am obviously biased, but I think it is better to own the car, because you never know what the weather is going to do, so you just take advantage of roof-off moments when they appear.
It doesn't tend to be something that you can plan ahead for (& thus book a car for)

cheers,
Craig