I play a fender strat (or should i say am learning) with a vox da5 amp that has several effects built in , and was wondering what difference a slightly larger amp would give me if any , what i`m saying is i here strats on you tube and they have different amps and sound very mellow compared to mine any thoughts?
Could be a mixture of the amp and pickups. What kinda music are the people playing? It'll determine gear and settings.
A slightly bigger amp might make a better difference if the sounds are decent. I know all you need is a practice amp if you're just learning so the bigger Vox amps like the AD15vt or AD30vt should be good enough for you. Try messing around with your Strat's pickup selector, volume, and tone pots as well.
buy a micro cube? effects and modeling! 'tis not bad!
Peavey XXX combo *upgraded screen resistors, Tung-Sol's, and 6L6's*
Schecter Syn Std. * modded, scalloped, and worn*
Schecter C-1 Elite *still sexy*
Ibanez AEL 12-string

"He who sticks his dick in peanut butter is fucking nuts"
Bigger =/= better, everyone. Getting an MG250DFX or a Spider III Halfstack would make his tone quite a bit worse.

What genres do you play, and what kind of money would you be able to throw down for a new amp?
to be honest as i`ve only just started playing and it`s only for my own pleasure so i don`t want to start spending even more cash just yet but when i do about £200.00
If you're just starting out I'd stick with what you have for a while. It's not an awful amp, and you'll develop a better ear for tone and playing techniques to sound better as you learn.