Arsenal could spend more? Not for any of the past eight or so seasons. We've been breaking even and that's about it; and that's as a selling club. Were our commercial deals shit and limiting the amount of money we could spend? Absolutely. Is the club and Wenger conservative with spending? Definitely. But in terms of the actual money the club can spend, that stadium didn't pay for itselfthe finances are pretty clear. As is, the club was only breaking even on the back of player sales and property sales.
Either the club could have a positive net spend and use that as a gamble to increase commercial revenue, or they could have zero net spend and bet on continued CL qualification to maintain steady revenue. Looking at how clubs like United have maximized their commercial revenue over the past couple years, maybe the board made a mistake in being so conservative (especially given the exorbitant ticket prices at the Emirates) but I don't think it's fair to say that Arsenal CAN spend and choose not to.
The only reason we can spend more this year is because of renewed commercial deals (the main reason our old ones were so bad was because we had to be locked in for long-term deals in order to have stable revenue when paying off the stadium) and the new TV deal. If we don't spend this summer, then yes, big questions need to be asked of those in charge. But taking on the investment of a new stadium right around when the oil clubs started pour large amounts of money and, financially, pull away from the rest of the clubs, into the game was just particularly bad timing for Arsenal and, well, the trophyless seasons speak for themselves.