I wish I was/were there

In this case, don't you think "I wish I had been there" would be more appropriate? 

you have to use "were" when talking about an "if" or "as though" statement.

 it's a non factual condition, and therefore "were" must be used.

the only time you wouldn't use "were" is when using the conditional mood,

such as saying something like, "I wish he WOULD BE nicer to me."

instead of the subjunctive mood and saying, "I wish he WERE nicer to me."

gwen stefani got it wrong, and the oscar mayer theme song uses it correctly.

just for some examples. :) 

If using "was" in counterfactual clauses is wrong, then many good writers of English are wrong. I prefer to trust the judgment of good writers on what constitutes good writing.

I wish my cold hand was in the warmest place about you - Jonathan Swift, Journal to Stella, 5 Feb 1711

I wish H. was not quite so fat - Lord Byron, letter, 8 Dec. 1811

I wish I was six feet tall and I wouldn't mind if I was handsome - And More by Andy Rooney, 1982

Some writers use both <i>was</i> and <i>were</i> close together.

...and all staring, gravely, as if it were a funeral, at me as if I was the coffin - Henry Adams, letter, 15 May 1859