So, car just failed MOT due to tin-worm in rear sills 
Having had the front rails replaced 2 years ago by MX5 specialist (great job Andrew Oulton) and at the same time new belts, waterpump, cambelt etc, and at last service yellowstuff brake pads all round, full set of stainless Goodridge lines, new alternator, new radiatorā¦
Iām sort of getting fed up with throwing cash at the damn thing.
While I love driving it, at nearly 100,000 miles is it REALLY worth it, or do I call it quits and sell the hard top and the rest of the car for scrap?
Whatās your thoughts???
Whatās next? Engine, gearbox, diffā¦!!!
Itās a crossroads for sure.
Only you can answer the question you pose.
Many of us have been at this point and some will have gone one way, the rest the other.
Personally I love driving my car so much that at the time it was worth the expense. Whether I feel the same in the future when it needs doing again remains to be seen.
Mineās done 143K and (touch a bit of wood) seems to be running well at the moment but itās not without itās foibles.
Doing maintenance comes with the territory of owning an older car (21 this yearā¦the car, not meš). Some of it is fun and inexpensive, some of it is irksome and costly.
What it comes down to is how much you enjoy your car.
If you can afford the repairs and look forward to sunny days of top down motoring then you might be able to justify the expense.
If cash is tight then things are probably less cut and dried.
It wonāt increase the value of your car enough to justify the cost but it may extend your enjoyment for much longer.
I wish you luck and clarity of thought when you finally decide whatās best for you.
Stay safe,
Guy
Race it, or put it in your living room.
I had the exact same dilemma. Had the chassis rails done, replaced the diff, and two years later all the sills (inner and outer) needed doing. At 120k miles.
If Iād known quite how much it was going to cost when I started, I may have not done it. But because I started spending money on it, I kind of felt compelled to continue.
Having said that, I do very much love my MX5!
On a more serious note, what year and model do you have?
If you have the finances and your car is worth nursing towards classic status, it could prove to be a good investment.
But in these uncertain times, most people would think carefully indeed.
Could you buy a car as good as yours for the cost of the repair? If not then Iād put the money into it.
100k is not the milestone it used to be especially for a Japanese car. Many of our mx5s have well over 100k, its usually the body that goes first it seems
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Totally agree here 
older cars do cost to maintain and keep on the road if you like yours to be top drawer. As BBB says, repair costs will/should be, way cheaper than a replacement car, that may itself become a money pit further down the line. Hopefully OP can get it repaired and enjoy, happy in the knowledge that they have a really nice example of the marque!
Barrie
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Your car is a known quantity with zero depreciation. Change to a newer one and
a It will depreciate
b It will need replacement parts
c It will rust.
Repairing yours is a hit financially and also be prepared to repair the rear arches in the near future. Itās your call.
The affair is over, scrap it and move on!..I know itās not really that black and white. The tipping point in scrapping mine was knowing that I could get Ā£500 for the Cat. Mind you it needed chassis rail and arch work, it didnāt owe me much and Iāve got another one, so not so painful.
Question is, how would you feel watching it disappear on the back of a truck? If the answer is relieved, get that cat off it now 
These were some of the arguments as to why I got all the work done on mine. My car is not depreciating on value, a brand new MX5 would lose in the region of Ā£300 a month for the first 3 years of its life. My 2003 MX5 has probably plateaued, and as such when all the rotten ones have died it will appreciate in value and rarity quicker than a brand new one would.
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As has been said, keeping on top of an elderly but enjoyable MX5 is most probably cheaper than the depreciation on a newer car.
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Thanks all - I am now looking at Mk3.75ās to replace my 04 Mk 2.5, as the car is also used by my wife and she wants a āmore reliableā one - not that mine has ever broken down or refused to start in over 4 years of pretty obsessive ownership !!
I am not looking for a quick-flip car, but a ākeeperā that I can clean and polish within an inch of its life!
However, never driven an NCā¦Will have to see if I can fitā¦ 
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Is it worth more in spare parts than a new good replacement? If so break it.
If you fit in an NB, you should fit in an NC.
if you break it, the mk2.5 cats are going for silly money at the moment
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And pre- 2003 LSDās
CAT & LSD togetherā¦whatā¦Ā£700/Ā£800?
plus Ā£200 for the VVT engine, Ā£300 for the 6 speed box, plus more if it has the bigger brakesā¦ soon adds up!
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Pretty much Ā£1,500.00 in scrap then if they rot out.
Not to forget the excellent hard wearing quality seats etc.
Blimey.
If it was a NA model, then itās probably worth keeping, otherwise I would not spend any mone money on it.
In answer to your question, as to whether you will fit a Mk3.75. I recently conducted an inspection and test drive of a Mk3,75 for an MX5OC member. I was concerned as to whether I would fit and be comfortable in driving it, being 6ft 2in but my fears quickly subsided when I conducted the road test, I fitted in and it was very comfortable to drive.