kev - we have this malarky every time i renew my mum's dla for her. i think its due to different people looking at the claims each time and coming to different conclusions to the last (and probably wanting to save a little money, too). yes you can appeal and i think it would be worth it as they are unlikely to stop the current low rate care component because you have high mobility needs and have recieved a higher rate previously.
in my appeals to the dla, i have always pointed out that nothing in my mum's situation has changed (and is just getting steadily worse) - so how can you (as the dla) reduce the rate. i also point out that i helped with the form and may have used different language and figures to support her claim, but that it is harsh of them to reduce the care component part because of this.
it is also worth pointing out that that care component also depends largely on who is helping you with your care and how much input they have. when filling out my mum's form, i always refer to my dad's role as carer when she feels particulalry bad (about 50% of the time) as a benchmark for the care that she needs - i'm not saying exaggerate, but make them aware of the full extent of your needs when you need it most.
also, you could approach your local cab or advocacy services for advice and support in appealing to the dla. sorry about the length of my reply and good luck in standing up for your rights!