Mine was like this an I managed to open it with the use of lots of WD40 and someone pressing on the front of the bonnet whilst I was pulling the latch inside. Took a while but got there in the end.
When you eventually get it open, give inside the mechanism a good spray with WD40 as they seem...
With that amount of miles I'd go with stripping it to get a bit of your money back.
I've been driving my other halfs 1.1 206 whilst trying to sell my shed, it's horrible to downgrade so much but needs must. Hope all goes smoothly with the baby!
Underside of mine looked like @bentwenty when it was lowered on AP's, subframe took a good battering but never had a problem with the sump.
If you really are concerned, as mentioned above, you can basically get a metal sheet to protect it which aren't too expensive.