Often times, a situation comes up and I want to use the expression "I wish!" For instance, somebody asks me: "Is that brand new car yours?" or "Was that you who I saw winning $1000?"

However, I don't think that simply saying "Ich wünsche!" is appropriate for this (of course I could be wrong, in which case please let me know).

So could someone please help me with a good translation for "I wish!" ?