Going to throw you a curve ball and tell you to go with both with a slight modification. I've have a set strobes for years and they certainly have their place depending on the type of shooting you're doing. I usually only use them at home in a studio setup but have taken them on location for portrait shoots and use them for station setups like step-and-repeat. In these cases the benefits you mentioned are all very applicable, but you overlooked the presence of modeling lights, which are really nice to have in certain situations. I currently have 3 Paul Buff Einsteins with a variety of modifiers. You're definitely on the right track with the Buff gear as far as bang for buck and quality. They are also a lot more portable than you might think. I have a single hard suit-case (maybe 25" tall) that hold 3 Einsteins, 3 Vagabond minis, 3 extra batteries, 2 types reflectors sets and various accessories. All I need to go with it is a bag with stands and umbrellas or other modifiers, which you would need with the speedlights anyway.
All of that said, I still decided to expand my speedlight capability last year to have 4 remotes plus an on-camera speedlight for event shooting and on-location portraits. The portability is huge for me, but the speedlights also offer a wider range of uses. You can substitute the speedlights for most strobe lighting applications if you can deal with the loss of power and lack of modeling lights. However, you'll find a lot more uses for the speedlights because of their size and the fact that you're more likely to have them with you. If you're shooting interiors, the speedlights can be hidden throughout indoor spaces to add light. If you're shooting portraits, you can use speedlights alone or in combination with strobes or even ambient lighting. You can do a lot of creative outdoor with with a fully portable and lightweight solution. My favorite application, however, is using speedlights to provide supplemental room lighting for large event spaces. I can deploy up to 4 speedlights around a room to beef up or replace ambient lighting. These produce very pleasing layers of lighting that set the images apart from a single on-camera flash. Don't underestimate the power of speedlights either. Here is a shot of a huge 3-story hall lit up with 4 speedlights:
I wouldn't want to part with either solution, so the next question is how to make all of it affordable. The AlienBee route is already about as affordable as it gets, so I suggest you get 2 ABs and a set of stands and modifiers (at least get umbrellas, which are quite affordable). Fortunately, you don't need to stick with the expensive Canon solution to build out a robust and reliable speedlight solution. I already had 3 580EXIIs with the 600EX-RT came out. I bought a 600 hoping to get improved eTTL performance (was marginally better) and then was left with the decision to buy up to 4 more for remote lights at a huge premium or come up with a way to make my existing 580s work. After a lot of research I invested in a set of Phottix Stratos II triggers ($90 for a trans/recv pair or $55 for recv only). With those triggers it doesn't matter what speedlights I am using, so I can go for a cheap option like a YungNuo YN-560II (same power as a 580 or 600 but only costs $73/ea). My current setup is a single 600 on my camera for front lighting, with a set of 3 580s and 1 YN-560 for remote lighting. The YN speedlight performs flawlessly and you can't tell it apart from the 580s. You do give up some functionality like remote eTTL (which I have yet to find a situation where I would actually use it) and you are adding extra gear with batteries for the triggers. The Stratos do "pass-through eTTL", so the on-camera flash still get all of the eTTL functionality, just none of the remotes can communicate like that. On the upside, the Stratos triggers have a 500ft range which is way better than the 600's 100ft range. For the photos in the link about, I would have been beyond the range of the 600s. The 600 wireless solution is actually more complicated by the way. You'll have to page through settings and make sure everything is communicating and it sometimes needs to be reset. With basic triggers like the Stratos, you just plug in, pick a channel and you're done -- more gear, but fewer options to worry about. You should keep in mind that with the AlienBee solution, you're going to need triggers anyway -- the Stratos work great for strobes, too. It sounds like you already have a set of speedlights, in which case, I would only question your motivation to use a wireless eTTL solution, especially considering the cost.
My advice would be to get an AlienBee solution and maintain a speedlight solution with low-cost options and remotes triggers. That by far gives you the most options and pro-level capability.
