There is loads you can do to these and still keep them looking factory, the Rover parts bin is fairly interchangable between models.
Looks wise if its not got the v6 splitter and skirts (asuming its a MK1) they are a must in my opinion to get it looking like its a bit lower. 17" wheels help with this too (MK1 straights or MK2 11 spokes to keep it looking o.e). If it doesnt have fogs you can add those and maybe put some 45 front lights on if you dont like the orange indicators.
Performance wise there is the usual air filter/ exhaust mods but on an otherwise standard 120 there is no point for the cost other than sound/ looks. If you want most bang per buck get a complete VVC cylinder head off a ZR/ TF 160, wiring loom and ECU which will see you to 158 bhp and is all plug and play for less than £500 easy.
You could then fit bigger brakes either straight off a 180 or use 620ti calipers with 180 front discs which gives you slightly larger surface area however you have to gring the carriers slightly to accomidate the slightly wider ZS discs.
There are loads of other mods you can do but that should give you an idea for now