Si B do me a favour mate, when you get your car back on the road take it out for a drive then go back home and disconnect 1 side of the ARB and take it back down the same road.
Your car being set up as a standard car is already under compression, so adding a compression strut kit will in effect only give you independant suspension and fixed adjustable castor. (or non adjustable castor if you compare it to the flexible springyness of the ARB).
If you feel you would like stiffer springs then like you say they are cheap enough to buy, but please dont go too stiff as with fully independant suspension on a road car you need a little lean on cornering to help give the road tyres the grip. Set it too hard and all it will just do is skate across the road in an understeering arse twitching moment.
People like Tim & Ian and other rally guys are massively overqualified in this subject and dont think twice of having a full package with a minimum of £200 rubber on each corner to help get the grip.
And its difficult to say this without belittling but a road car with £80 tyres on will indeed notice a massive improvement under braking and cornering, but it will not save you the extra 2 seconds per lap that these lads will have with their WRC stuff.
Start somewhere and use it as a base point.
I have spent hours and hours trackside with both rally cars and racing cars, the number of times the driver has come in (with stiff suspension) on a damp or wet day and asked us to disconnect the ARB (front or rear) or reduce its stiffness if bladed to make the car turn in, or handle better sometimes really does make you realise why the propper cars had driver adjustable stuff.
Whilst it is very interesting to read all the input on this thread from qualified people, it also needs bringing back down into road car level to someone who is making first steps on the ladder
Do it, try it and report back please. If you need help ring the guy who made your road car kit, you have his number and he is more than willing to offer further advice and support. Buy the same kit from other trade outlets and most will just ask for an order number, a credit card number and a postal address and thats it. I know for a fact that well in excess of 500 of these type of kits have been sold over the years to people like you. If they were no good and needed massive mods they wouldnt still be being made and used.
I wonder if Tims Sunbeam will have WRC parts on it, and if not will he refuse to drive it ??