There are all kinds of factors at play here, none of which I have any concrete data on.
First up, there are probably way more console users than pc users. However, a percentage (not a majority, but certainly significant) of those would be kids whose parents buy them one or two games a year.
OTOH, PC gamers tend to have more disposable income (based on the fact that they have at least a pretty decent PC). Plus, steam sales come up all the time and lots of PC gamers have massive libraries of games they bought cheap and never played.
All of these (sometimes conflicting) factors make it hard to tell who spends more.