I don't see a problem, especially if you've got a raised bed with good soil. When's your frost date in Broomfield? Colorado State Extension says to sow 4 weeks before the average last frost date. Ideal spinach growing weather is 50 to 60°F. If that's the case locally, I'd go for it.

Just be sure to plant them behind some critter-proof fencing, though. ;)

I went ahead and planted them this AM. I had sown some seeds direct about 10 days ago, but the baggie seeds beat the direct-sown badly.