I don't have a the budget to buy any high end pieces, but to me I would always choose the older piece. I have a few reasons:
1. Jack Kirby passed away and there will never be anything new from. While Kirby produced a lot of art, there will always be new Jim Lee art (assuming he continues for the next few decades).
2. Old art won't see the significant potential drop in value that new art could. For example, if you bought a high end Liefeld page when he was hot, how would you feel about passing up a Kirby page? (This is just an example...we all know that Lee is no Liefeld.)
3. While you may love the new art, that art may just be a typical page 10 years from now. ("Oh, another angry Wolverine cover....")
4. From a financial standing, a book or title may be considered insignificant in the future. (We love Hush now, but if no one cares about it 10 years from now that page may be significantly less valuable.)
There are many that are far more knowledgeable than me, but these are my thoughts off the top of my head.