Welcome to Flyertalk NirE, welcome to the British Airways board, it's great to see you here. Please feel free to participate fully in this community, we try to be welcoming to newcomers. And I hope you have a good flight.

It is the case that ordering special meals will greatly constrain your chances for a free upgrade, though not a paid one. However if you don't have status with BA your chances of that upgrade are not high anyway.

I have heard of cases where they have upgraded someone to CW but indicated they will get their original rather than CW meal, which seems fair enough; but I gather that is unusual and probably going to happen at the smaller out-stations where word of mouth can over-ride Standard Operating Procedure.

In CW there is always one vegetarian dish available - and if you are genuinely a vegetarian you best indicate that as soon as the menus come out - whereas in WTP the menu is far more restricted. Which doesn't make life any easier for you, so unless you are prepared to take food with you just in case, then personally I'd stick to your special meal and WTP: at least you know what you are going to get.