I'm adding very little to this compared to what has already been mentioned but:
-Rarb absolute best bang for buck mod, cannot praise it enough. I got the whiteline rarb (BWR19Z is the code for the one for our cars) Some people get H&R. Whiteline is the one I have.
I would 100% put a Rarb on first and go from there.
-Suspension, ask him what springs he has, how much of a drop they are, brand etc.
On standard, original shocks and springs my monte would often bottom out on some of the roughest parts of our roads (albeit at first only when I was going ""quick"") eventually they got to the point where the shocks were completely gone so I put coilovers on mine. 20-25mm drop, the car handles itself very well and no more bottoming out. If your cars reaching around 100k miles theres a good chance the shocks won't be performing at their best and it would be pointless putting lowering springs on worn out shocks.
Tyres- your car will have 205/40 R17 tyres standard, thats one size smaller than the equivalent ibiza/polo. Going up to a 215/40 to match the sister cars is a no brainer. Bit more tyre on the road and a slightly fatter sidewall to soak up the bumps better. Plus a 215/40 fits the rim so much better than the 205/40s.
Bushes- If its on original bushes they might be wanting to be changed at this point. I replaced all my bushes with polyurethane but thats just me. I'd atleast do the wishbones with polyurethane bushes.
Brakes- Standard brakes are decent especially if you have quality pads. I changed my front brakes to 312mm ones and have no regrets in doing so. Rears do very little in comparison and your vRS has rear discs already. They can be upgraded to 256mm vented rears but again, it won't make as much of an impact as upgrading the fronts will.
I'm in the process of converting my monte from drums to discs, think I have a set of 256mm vented rear brakes sourced but if that falls through it'll just be 232mm solid discs same as a vRS.
While a Monte (Especially a diesel one) is different to a vRS, the basic handling upgrades will be the same.