There are a lot of poorly coded themes that are free which will keep you back in my opinion. With that being said, if you don't look at obtaining the knowledge of what poor code verses good code is, DreamWeaver isn't going to help you the least bit.
The cost of ownership is $399 (may be coupons, I'm seeing a returning user [possibly cookie] bringing it down to $299) for the
Genesis Framework and all child themes on unlimited sites that you can develop and have full rights to sell or develop for others. There may be coupons out there knocking the price down.
The framework boasts increased speed and security. Once you learn the ins and outs of it by following tutorials or guides by 3rd parties, you're good to go.
I think twice the price of DreamWeaver is well worth it with ~30 HTML5 themes and ~45 total.
I'd suggest Yoast for SEO and W3 Cache to speed your site up. They're both free, taking down your cost of ownership on unlimited sites which would save you time.
Time is the most expensive commodity in my opinion and you're going to spend much more of that learning DreamWeaver than installing themes which can take minutes.
Whichever route you take, good luck.