Of course it matters what wattage you get, Too much and you will blow your subs, Not enough and you wont be happy.
The wattage is shown in WRMS, Which is Watts Route Mean Square. Its a proper way of measuring actual power, AS regards to sayings I have 10,000 watt stereo.
However, IF i was you, I'd just buy this:
http://caraudiosecurity.com/shop/product/products_id/2955.html
Its cheap, A good amp, And will put 580wrms (290wrms to each sub) When wired to show a 2 ohm load. That Figure is at 14.4v however, So id say the actual WRMS figure on a Clio with battery and charging system is closer to 500wrms.
Either way, ITs a good set up that is tried and tested.
Not saying this is the only amp that will work in your application, buts a very good contender.
Was quite interesting, Back in my chav days, I pulled into a McDonalds, Blasting my music, And there was a group of People with their systems blasting, And I was clearly louder than them.
I parked up and got out and a few came over to me asking why my stereo was so much louder, They had 2 Xplod 12" subs with 1400w writte on them in big letters, I had a M1001, Putting out 1000wrms to 2 Alpine Type X's at the time, And They wouldnt have it that I only had 1000w and they had 2800w and mine was louder lol.