As NM said, how much are you prepared to pay? I've been Pt for years, and it's very nice - often upgraded from business to first etc. But look at the realities :
1. 1st class check in - might save 5 minutes compared to business.
2. 1st class lounge - very nice in Sydney (over the top). LA is usually less crowded etc. Many airports don't have a 1st class lounge. All I need is a comfortable seat, quiet, drinks and a snack.
3. Occasional upgrade business to first. I rarely fly economy but maybe upgrades are also likely.
There are other benefits, but none that really matter to me.
How much would I pay to go from gold to Platinum? $100, $500, $1,000? If I was sure I would do a lot of flying in the following year, I might fork out $200 on an additional flight just to get to Pt. Otherwise, I'd settle for gold, and spend or invest my money somewhere else. Your choice on how much you think it's worth.