As Xeyska said, any sort of investment comes with potential risk, but it also comes with potential reward. When you put money in the stock market, you do so expecting it to grow, but there's the chance you may lose it.
The risk in this case is that the game slips more or never actually launches. While schedule slips are very common in software development, especially among small indy teams, I at least feel very confident about the current schedule. I came to the game "late" (a few weeks ago) but I've been reading/watching old Q&As and dev journals and things feel much more certain now. In the July State of Elyria Caspian mentioned that since December they have expanded their engineering team by "several hundred percent", so it sounds like SBS has certainly made the investment to be successful. I forget where I read it (I thought it was the SoE, but I couldn't find it in there), but he also recently said that when they started they did so under the assumption that they would be able to grow the team rapidly, but that didn't happen. It took longer than expected to find the right talent, but it sounds like they've finally found it.
Jousting has been such a big thing lately because that's what they wanted to show off at PAX West. It's hard to demo an MMO, especially one that is still pre-alpha, so they picked one thing and focused heavily on that. I'm hoping that over the next few weeks we'll start seeing other new content.
So now let's talk about the potential reward of investing. The reward is that you help CoE become the reality that you are hoping it becomes, but on top of that each tier has other perks such as mounts, titles, custom surnames, etc. The reason SBS was able to add so many new engineers is because of the backing of the community. If everyone sat on their hands saying "I'll play it safe and wait until it comes out to buy it" then it never would have gotten off the ground. If you are certain you would play the game when it finally does come out (i.e., if you're willing to pay the money anyway), then IMO you should go ahead and invest.
I'll make it personal for a sec. I started small. My initial pledge was Pioneer ($70), but each month I'm putting $20-30 away and slowly upping my pledge over time (currently at Bloodline and my goal is to eventually reach Mayor). That's $20-30 a month that I could be spending on other games and things I enjoy, but frankly I don't want to wait for CoE any longer than I have to, so by upping my pledge I can get earlier access to the Betas and Alphas.
Personally, it would hurt me to drop $250 on a game right now that I wouldn't even begin to play in Alpha for another year, but I'm effectively only spending about $25 a month on it. It also helps keep my excited about the game and I'm finding other ways to enjoy it until I can play it, such as getting involved in the community and even writing fan fiction. I wouldn't do any of that it I wasn't invested in the game.
*waves pompoms*