Boy, I'd say just the opposite... sorry Rob.
The amount of money you will lose on buying either one of those boats is minimal, they aren't going to go up or down in value very much, in contrast to say a new boat, which like a car, will depreciate immediately.
Go for the big one - sounds like you need the space and the paddles. It's going to suck going solo, but if you are really into that you will want a smaller, lighter boat anyway.
I'd say just go for it and plan on selling it within a year or two if you plan on keeping going (or keep it as a spare for friends or as a beater). Then look for something that will work better as a solo boat. I'm pretty sure you'll be able to pass it on for near what you paid for it.
I don't often promote the Raddison but for a small, solo fishing boat, it's pretty good. I hesitate to call it a 'canoe'. Depending on where you live you can usually find a good one between $400 and $500 with the seats and paddles. That could be your 'solo' boat. No technique required, you can row them. The biggest advantage to them is they are light and stable.
Get on the water, then you'll really appreciate the next boat you buy because undoubtedly it will be lighter or better performing which is not hard to do from where you are starting.
I went from the proverbial horse and cart (Radisson 14') to luxury sports car (Swift 16') myself. I quickly realized if I was going to go more places and spend more time on the water I was going to need a better tool for the job - so I shelled out the loot... and I did again... and again... and I'm sure I will again in the future. But I love having a spare boat, and I love having a light boat, and I love having a solo boat... and that was the price of admission