Yes, very nice though the Tamiya Spitfire kits are, do we really think they justify the high price tag?
Maybe, maybe not, but as I generally prefer to show the aircraft in 'clean' configuration, that is, with all cowling panels and hatches in place in the 'closed' position, with the probable exception of the canopy and cockpit access hatch, all those extra engine, ancilliaries, gun bay and other parts would be wasted on me (unless built specifically for a diorama or similar), so I'd be paying a lot extra for parts not wanted or used.
I think I'd rather pay £20 for a good kit which fits the requirements, than £120 for an excellent kit which by far exceeds any requirements and leaves a large proportion of the parts unused.
Also, Revell have a very good recent history of being able to provide a kit that has most of the engine and internal detail, at a far lower price than some other manufacturers, which still allows a superb replica to be produced, out of the box, and with the possibility of purchasing separate detail parts, or scratch-building additional detail if required, and still bringing in the total cost at a much, much lower price tag.
Nothing wrong with the Tamiya kits of course, but £120 against £20 ? I know which I'd go for in this instance - especially if Revell release a Spit MkIX, which may be on the cards, judging by the 'multi-Mark' description when the new Mk1 was first announced as a 'Future Release' on some web-sites.