Well, my NC is 14 years old now, and maybe time to move on.
But I’m getting too old to be crawling underneath every year to check for rust (and fix it!), and my ability to ferret around with trombone cleaners to keep water out of the car is decreasing with age (Mine)!
So a question - is the ND plagued with the same sorts of problems? (See my response to the “Most Reliable Car” thread for background)
Well you don’t use trombone brushes to clean the roof drains on the soft top ND! See “ND Roof Drains” thread and others. Both the ND’s that I have had have been utterly reliable. But they are/were relatively new cars. I would not think that any MX5 is “plagued” with reliability problems. They have consistently been one of the most reliable cars on the road. Early ND’s with the 2.0 litre engine allegedly had some problems with the gearbox (in the main, cars used for competition) and the gearbox has been incrementally modified by Mazda. Most suspect gearboxes would have been replaced by Mazda under warranty by now. A sometimes reported problem with the NC is engine problems if the oil level is not maintained at nearly max.
I think it’s early days ref ND rust. Given the general lack of rustproofing at the factory, and the recent change of tactics regarding “not guaranteed against road salt corrosion” it’s probably fair to say that at some point, if neglected rust will start.
May be an idea to be as new as possible and get it treated by one of the many specialist if you intend to keep the ND for a while?
Another point to note is that I would imagine the ND is a different animal to the NC?
We have owned a Mk1, Mk2.5 (for 17 years) and only recently changed to an ND. We gave the NC a miss for no other reason that we loved the NB and were just about getting our heads around changing it for an NC when the ND came out, and to be honest I just preferred the looks of the ND. The ND seems significantly smaller than the NC so may be worth having a test drive to see if you can live with the lack of space first?
…happy decision making!
Forgot to mention, as you have mentioned the scuttle seals in your response to “Most Reliable Car” thread, they are a different design in the ND and no longer penetrate the bulkhead like the NC.
Also most modern cars are supplied with a cr*p puncture repair kit instead of a proper spare to reduce costs and weight. It would be a last resort to use one of these as the repair is only temporary and once repaired using this stuff the hole in the tyre cannot be plugged in the usual way. Lets be honest most punctures nowadays occur from hitting pot holes and the like which tears/damages the tyre sidewall rendering it unrepairable.
In my opinion the mx-5 got its mojo back with the ND; sharp, modern styling combined with excellent engines and drivetrain. I have the 1.5 engine which produces plenty of power for normal driving on UK roads and is economical and characterful. The 2.0 offers more go if that’s what you want. For the money it can’t be beaten for pure fun and enjoyment. No issues for me in 2 years of ownership, bearing in mind limited use due to lockdown. Rust wise I think they have used some better materials in places, but being a mazda there are likely to be issues down the line for older cars.
It really depends how long you intend to keep it and how you care for it while you do have it.
If you’re going to own an ND from year 8 or so onwards I’d want it to have been undersealed, I’ve done both ND’s I have owned from new, it may help with selling it on too, if it’s not a keeper for you, that you may realise more value from an enthusiast.
If on the other hand you’re only going to keep it 2 or 3 years why bother, let the enthusiast buy mine with the documented underseal 
I worked at a Mazda dealership when the NC first came out and demo’d them to many potential customers… I thought these and the earlier NB’s were fine - We still had quite a few NB’s back then too… But my first and current MX-5 came in the shape of an ND2 2 litre, and in my opinion it is a “return-to-form” for the MX-5… Took a while to get used to how then headlights looked… but now, a few months on… I love the ND 
I’ve had 2 NCs and I am now on my 3rd ND. The NCs do have more room and also a glove box 
The ND drives more like the Eunos / Mk1. I’ve not had any reliability issues, the only issues I’ve had are the roll hoops rubbing on the roof and wearing it away and rust on the door quarter light window pillar, both recall items and both fixed under warranty.
I love the fact that still happens with MX5’s I remember treating the same problem on my old '91 mk1
The ND does have a glovebox…just that its between the seats and a bit of a pig to access while you are sitting in it!!
(Would have been better if they had not bothered with the CD player and given you the space…or at least made it an optional extra!)
On the soft top ND, do you also have those tiny compartments that don’t lock, one behind each seat?
I’m sure I’ve got storage compartments behind the seats on my soft top ND. Don’t think the RF has them because of the “mechanics” of dropping the top…
…yes on the soft top there are 2 small compartments behind the seats…difficult to access as you need to get out of the car and move the seats forward…but better than nothing!
There is one behind the driver in the RF
As well as the lockable compartment between the seats? I didn’t know that.
Sitting in your glove box, I’ll have to try it. 
does it have a latch on the inside - in case you cannot get out?
Yes. There is one behind each seat in the soft top ND. I have put the puncture repair kit (rather than taking room up in the boot) and other things that need to be with the car but will be very rarely required in these cubby holes.
Excellent idea Ralph! 
I’d never thought of that, and you can access those bits of kit without emptying the boot if it’s full! 
Yes. And that as well!