Well... It's REALLY hard to judge. Gold could continue to go up in value, but if you look at a historical track, my guess is we may be close to hitting a plateau? I'm no expert, for sure - but if Gold drops in value (and it will, I can't tell you when - a month, a year?) and suddenly your Gold collection is worth half as much as you paid for it, it'll be a lot harder to explain to your wife. Of course, over time, it will obviously recover any losses and accelerate to a solid investment.
My thought there is talk to your wife about it, explain your thoughts, and if you want gold - go for it! Understand there is some risk, and keep your portfolio well-diversified.
* AGAIN - I'm NO EXPERT... just thoughts of an amateur. =) I could be COMPLETELY wrong! *
For what it's worth, ME- I'd probably go for better copper key dates, maybe not break up my set, but invest in a few more (extra), for now... then when and if gold ever does fall, you can pick up more of it for less, and keep your sets complete. But that's only if you want to put money into your collection that you don't have in it. If you want to go through your collection to raise money for new acquisitions, I might stay away from gold for now, or make some modest investments and ride the short term train, selling periodically to make sure I recoup what I can - then if the price does plummit (or even drop modestly), I'm not caught with my pants down and I've got an even cooler collection that I didn't lose too much on.
Anyway, I'm rambling about theoretics here now. I'm no expert, I'm an amateur, and I probably don't have any idea what I'm talking about!
As others have mentioned, eagle1 - you do have to account for a spousal tax associated with collecting and playing with toys of any type. So if getting a few gold pieces appease the spouse, that's a pretty cool situation to be in!