I agree with PSJ and everyone else on this one.
I know how fustrating it can be to try and get the time that you want. But the real trick is mastering the setup that you have before taking the next step or buying new stuff. I thank PSJ for really highlighting that for me.
Yes you could probably invest more money into the car and make it faster then what it is now, but you would still be leaving the possibility for improvement on the table.
Focus on practicing and getting that 60ft down. I too ran a 1.72 on 18" drag radials -with stock gear, stock suspension,and stock rear end... so you with slicks should be able to get numbers even lower then that. So i see that as the biggest area of opportunity right now. Don't look at any other number on that time slip until you get the 60ft down. It took me several trips and passes at the track to lower my 60ft. I started at 1.9x's and now have the right feel for the launch to where i am confident now. Thats all it takes is more seat time really.
just my .02's