Yep definitely see if your school can offer them at all. If they don't, pester them until they introduce it
The idea of AEAs is that they're based on what you're normally studying for your A level but harder questions ie you don't have to do any extra revision. As I saw it they wouldn't take up too much time as it was just a 3 hour exam and a couple of past papers to practise. It's difficult to put a measure on how hard they are, it's harder reading and listening comprehension, fill in the gap exercises, probably some rephrasing exercises and a 500 word discursive or creative essay (if I remember rightly!)
The best way to see is to have a look at some past papers. OCR does the French and their website seems to be pretty rubbish and doesn't have any past papers but there is some related info here
http://www.ocr.org.uk/qualifications/aea/french/documents.htmlIf it helps the Edexcel website has a specimen paper for Spanish here
http://www.edexcel.org.uk/quals/aea/9881I'm sure you could find some actual past papers if you google it. I actually think I may have got an old French paper off our very own TSR so search the language forums here as well!
As for marks, I don't know whether you can decline it but I guess you can just choose not to put it on your UCAS form. And yes I'm sure they will be impressed with a merit - I got a merit for French and a distinction for Spanish.
I asked about AEAs at an open day I went to before applying the second time. They said they looked on them very favourable and it shows you can bridge the gap between school and uni. They also said they'd give a medal to anyone who got distinction in physics! Ok so we're not doing physics here but that shows they do value them.
What else? Oh yes, I was pooled the first time...although I slightly suspect I was automatically pooled as I fitted the criteria, who knows. And you're right, it's definitely better to apply to a different college, clean slate and all that.
Anything else, just ask!