It seems (in my view) that Mazda in their wisdom of saving weight to the nth degree have decided that they can't easily fit a space-saver spare wheel in the area below the boot floor, and therefore possibly wish to 'discourage' potential buyers from having one fitted in a specially-built new floor, especially if the extra weight reduces performance and mpg.

I still think whatever the reason, they are being increadibly stingy in not offering it as standard or at least at a reasonable price comparable to most other makes (often a third less at least), and will deter potential buyers of pre-reg cars (as I wouldn't be surprised if the dealers who do this don't spec the spare wheels), myself included.

If I were you, I would get one (if you can't back out of the deal without incurring a penalty more than half the cost of fitting the [space-saver] spare) as it will definitely be easier to shift (not necessarily any higher 'book value) than a car identical in all other respects without it. No-one will car about the 0.5 mpg less or 0.2 sec more to 60mph, but in my opinion will like the reassurance (as you seem to want as I do) of having a better backup than a poor can of glue (HJ isn't impressed as far as I recall) to spray into the tyre in the event of a puncture (which will probably render it useless to repair if it could've been without the innards filled with the glue.

Both mine and the wifes car came without spare wheels, the dealer wanted £300 for one and £200 for the other.

Instead I went on www.mytyres.co.uk and it cost us about £70 all in for a wheel and tyre fully fitted delivered to our door. Click on the link on the left for "wheel and tyre packages", choose steel (its good enough for a spare) then find your car in the drop downs and it looks like the cheapest for a CX5 is about £110 + £10 postage.

Both ours took about 4 days to arrive and were perfect. Just added a jack for another £10 and we are sorted for a fraction of the manufacturers/dealers cost.