DeborahAnnabeltoo - it may well have been his dream as well. But it was still her who was dying, she was having the dream - it is her who says 'this isn't real, we are in her perspective. And this was a 'kindness' he was doing for her "after all this time do you really think I would let it hurt".
So... if she doesn't want this intimacy with Dracula, if it's what he wants - then his act of 'kindness' is a violation of her in her last moments to give him what he wants. And whilst that might be true to what Dracula is - it's not a good ending for Agatha and they shouldn't treat their female protagonist with such male centred disrespect.
It's better if she is a nun with a crush - because then at least this is what she always secretly wanted.
However I don't think she was at all presented as nun with a crush in the first two episodes (if anything she was into the boat captain) so this ending was weird and came out of nowhere. A romantic ending to an intellectual relationship between equals where the characters- even though enemies - respected each other. They wouldn't have done that with a male Van Helsing.
I think that drinking blood regenerates them to the point at which they became a vampire. The point at which they turned into a vampire is the best face that they can present to the world. So, for Lucy, her partially cremated body was what she was stuck with
They never actually said as much though did they? You've head cannoned this (and it's sensible headcanon) to overcome a gaping plot hole - but canonically the plot hole remains 
If Dracula himself became a vampire as a young man, then why does he grow old in vampire form*? If he became a vampire as an old man why can he become young but Jonathan and Lucy can't fix themselves?
I'm not sure this is ever explained in the book - it's been a long time since I read it. Maybe - being the first real vampire book and before all the lore was set down he was immortal but not eternally youthful, but could regenerate to youth by drinking blood. (This doesn't explain why he lets himself get so very old in the first place and why he isn't continually regenerating unless he hasn't drunk human blood in decades when we first meet him.) But* even if this true for the book - it falls down for the programme when he spends 120 years under the sea and is fine. Without blood he should have aged. 'Comatose' doesn't really cut it as an explanation - people in comas still age. and 'regenerating so not ageing' just throws up more questions than it answers. If all it takes is a box of soil to halt the ageing process (no blood necessary) - why did he need Jonathan Harker in the first place? How did he ever get old? He always had his box of dirt handy.