Apart from the mentioned problem with keeping the threads clean, are there any other drawbacks to consider ?
How long would a set of coilovers last till they are no longer adequate (ie used up ?)
I have used coilovers on my primarily track car - also used on road. Done over 10k miles, no problems.
I smear copper grease over the threads to help prevent corrosion.
I can remove, put new springs in, clean and re grease and re set up in less than half a day, they are easy to work with and the most verstile option.
They can be rebuild by the manufacturer for about 40quid each. Another bonus.
Adjusting the ride height - when you look at weight transfer and as you progress in trackdays in terms of skill and knowledge of the cars setup you will naturally want to make adjustments to the car to make it better. As an example, being able to raise the back 10mm (which takes less time than the lunch break at a trackday) will help resist weight transfer to the rear and can bring on a bit of oversteer (if only lift off oversteer) which you can use to help you turn in the corners better. This is just one example, there are many reasons why you may want to adjust height, or simply for setting up on corner scales.
As for too hard for the roads - simply order different spring rates.
The problem with most of these suspension kits is they just uprate by xxpercent, many suppliers couldn't even tell you the spring rates.
A far better option is working out what suits you best, and order the springs that way.
You can always change the springs if not quite right, they are about 20quid each for faulkner springs, or try touring car spares for eibach used springs.
Depending how hardcore your trackdays are, you could even change the spring rates for the trackday. If your running slicks you may want to be close to 1000lb springs, but for a smooth ride on a rough road, 200lb could be better.
I run 800lb on the road&track, its firm but not unbearable, but many people wouldn't like it this firm.
Coilovers will be too much hard work if your lazy, got two left hands and would rather stand around talking about how good your car is.
If your willing to put in some effort, maintain them (remove and clean once a year) and want the best out of your car in terms of handling - if your doing trackdays I assume you do? then coilovers are the superior option.
Combine this with adjustable camber and your car will handle like its glued to the road.
I was on a trackday weekend just gone, and could get round the circuit no slower than a vx220 turbo & 400bhp per ton superlight r400 driving a crappy British made 4 door saloon car. No-one else could do a lap of the circuit quicker that day. Other than suspension setup, the car is standard and could outpace some real machinery. That's how important a well setup car is on the day. It pees a lot of people off, especially those who put their money into big turbos, remaps and big power outputs, but failed to even look at the suspension setup!
I don't know who makes what for alfas, but GAZ coilovers come in at around 500quid. They are good, sadly though they have been bought by those who don't look after them, and when they corrode and seize shout loudly about them being no good. They are used in many race series, the guys broke away from a large specialist well known & respected suspension manufacture and set up GAZ, so they are not short on knowledge.
If your budget is 800quid, I would go this route and use the remaining money to sort out the camber with adjustable arms.
Right now, you may not think you need coilovers for a trackday a month, but I think you would regret not getting them in the future.