I haven't played T20 or any of the "new d20" games. In the old days of D&D half the fun was building up levels + HP so you could stay alive, as combat whether via swords or spells could get nasty, especially with 12-20 hobgoblins coming at 4 party members. It was a given: as you rose in levels, so would the opponents.
One thing I've noticed about Traveller (especially GURPS) is that you can die from a single weapon wound, of almost any type. Which brings out the "hey this ain't D&D where you charge head-on into danger!!!" realization.
No magic armors, and with GURPS specific weapons designed to defeat certain types of armors can really change the odds and make PCs take stock of what they're doing or about to do.
None the less, I think the odd firefight is essential, especially if you're a mercenary character, but also the interaction of sophonts with the setting is complex that you also have to spend a significant time doing mundane things (like making sure you have enough money or getting from A to B) that you have to think about more than just shooting things up.
However as a GM I'd pace sessions depending on their frequency, meaning I'd introduce content of sessions based on the available gaming time, so that we might fast-forward thru certain mundane portions, touching on them in passing and reserve what I felt was the basis for the adventure for the focus of the session.
Sometimes people like haggling and shopping, sometimes they don't.
