There are various levels of "regular" people, you could almost classify them by ADD rules such as "regular curious",
"regular neutral", "regular adverse to learning" and so on.

> By comparison, those individuals I see who are willing to learn new features or who can notice what they did to set off a feature are usually pretty tech-savvy (or soon will be) and would be able to figure out how to use and install extensions anyway.

Those would be the "regular curious". Sure they could figure out by themselves how to install extensions but why would they? Before speed dial nobody felt the need to have such a feature (so why search for an extension?), but now a lot of people can't live without it (same for multiple tabs, sessions, mouse gestures, integrated search, closed tabs bin, and so on). Until you have a feature at your finger tips you will almost always not feel the need to have it, thinking "meh, I can live without it". Once you start using it your perspective changes.

Basically, a regular user who always had a minimalistic browser will hardly feel the need to go looking for extra functionality except for dire cases (ad-block or something). So the fact that he is technically capable of installing extensions is a moot point. He first needs to become aware of that functionality and the process of testing it out should be easy enough for the curiosity to surpass the "don't need it" feeling. Sure, you could live with just a unique tab and an address bar. it's nice and minimalistic. How many regular users would bother installing extensions?

> Then again, a good number of the people I do know don't even understand the concept of a web address or even how to use bookmarks -- nevermind speed dial.

These would be "regular adverse to learning". But seriously, have you ever used speed dial? It's much easier to use than bookmarks. I explained it to a lot of regulars in 50 words or less "click the 'plus' button, enter the address of a website you want to visit later". It's difficult to explain this to people who can't quite hold a mouse in their hands but for regulars like my mother, girlfriend, whoever, it's very easy to explain.

Let's take the case of my mom. First I showed her how to open Opera instead of IE. Then, after she got used to it, I showed multiple tabs. Then, after a while, speed dial. Then I moved the tabs on the left side so that she had more space. In the case of my girlfriend I also showed her RSS so that she wouldn't check every day for new blog posts.

The trick is to introduce these features/changes gradually, depending on one's level of comfort with technology. At one point I actually managed to get a person with a rather ossified brain to use speed dials and multiple tabs.

Obviously, if a person were using a browser without a certain feature then I wouldn't go about installing extensions for them. For one, I would have to search for a decent extension since their quality is most of the times inferior to the out-of-the-box feature, the user would most likely receive strange notifications about them and wouldn't know what to do, they could pose a security risk, and so on. I'd just say "oh, you're using browser X? I could try installing an extension... ah, screw it. Carry on with business as usual, searching on google the website that you visit 10 times a day".

> So personally, I think it's a good idea to aim for a default, minimalist interface and avoid gestures and interactive UI elements that users can accidentally click or activate.

Well it's not a mutually exclusive affair. Opera has a truckload of features and a minimalist interface. The speed and resource consumption are as good as Chrome's (and much better when large amounts of tabs are involved, because of the one-process-per-tab slowness). So what is the reason for choosing Chrome over Opera then? Just curious.