Why not both?
I mean, if you can indeed make it street legal, you can do navigational rallies, too...
Look up "time speed distance rallies" on Google to find some near you. They're less likely to break your car, and therefore also less likely to break your wallet.
Tuning advice: weld stuff. Weld your rear strut towers together with steel tubes. Install a huge roll bar which can easily be removed for gravel stages... Or snow. Do you get snow?
Buy a front strut tower brace bar, which can be easily removed (unlike the rear one).
Buy a reinforced subframe thing... It'll bolt right up to the existing stuff. In conjunction with the cage, rear strut tower bracing, and front strut tower brace bar, it'll be faster on every surface you'll drive on.
Don't skimp on tires or brakes; these are super important.
Don't be tempted by overly pricy coilovers unless you absolutely need them. The money you could save with super high quality struts and springs makes up for it.
Have winter/gravel rims and summer rims... The winter rims should be narrow, and have narrow off-road (snow) tires mounted. The summer/pavement rims should be 235/45R17 if they'll fit, or even 245/45R17.
Get roll bars first, and then buy springs and struts or coilovers in order to balance out the handling with the roll bars... Sometimes, because roll bars make the biggest difference, people will regret buying the springs they bought, because the roll bars made a bigger change than the springs, and suddenly they've gone "too far" with their setup. For example, before I got my rear roll bar, I had understeer. I would've gotten some super stiff rear springs. Then, with the roll bar, I would've had way too much oversteer. Even with OEM rear springs, I've had huge problems with oversteer.
All if this is irrelevant, however, if you get adjustable roll bars; best decision I ever made.