Galactic Wonders

Yes, you must permanently sacrifice a tile which cannot be reclaimed.

I often dedicate a mid-high PQ planet with no bonus tiles to warehouse my wonders in (I buy more than I build) so as to avoid cluttering more productive worlds.

I notice you can trade the wonder's abilities to others so I was wondering whether I really had to give up all that space to wonders.

Only trade goods can be traded in this way, not wonders (though they are similar). Wonders only benefit the person that built them, while trade goods give a bonus that you can share with others. But if you built the trade good and lose that planet, you lose the bonus from it.

Both of them cannot be demolished, so once you build them you're stuck with them (unless they get destroyed by a damaging invasion tactic, at which point they are lost forever).

Thanks for your answers, that helps alot. I'll be more careful with which wonders or trade goods I grab. Or maybe I'll just buy the trade goods.

Again thanks for your time