I thought long and hard about that, playing around with a variety of ideas including going back to the 3.x model of a single hit die at 1st level, having hit points simply be equal to your Con plus your Con mod every level, or just having static HP and getting rid of level-based damage bonuses, and so on, but I finally decided there was enough "in-genre" justification for higher level characters being more durable than lower level characters, and for that matter for "heroes" to be more durable than "non-heroes" that I would stick with the SWSE model.
That led me to think about what I wanted to do re: nonheroics, — not to mention determining experience points. Mystery/horror is not a genre where the characters are expected to go up against "four level-appropriate encounters per day and then rest." Generally speaking, mystery/horror characters can expect to wander around doing research all day and then have a hella-deadly encounter in the abandoned mine at midnight. Similarly, NPCs are generally information-vending machines (in which case their stats are irrelevant), monster fodder (in which case their stats should be easily-shreddable cheese), or plot-immune until their scripted destiny (in which case, again, their stats are pretty much irrelevant).
In SWSE, nonheroics get 3.x-style "one die per level" hit dice (and don't even get the full die at 1st level), do not get level-based damage or defense bonuses, and don't get talents. However, they can multiclass into a heroic class to gain access to talents -- making an NPC "nonheroic 1/scout 2" is how you would make low-level wilderness guide who was competent but not as slick as your 3rd level character party, for instance (and who could be quickly eaten by the monster without having to worry about all those pesky extra hit points that keep heroic PCs alive).
This game doesn't have talents tho, it's all skills and feats. So I'm thinking that for my nonheroics, I might stick with 3.x-style hit dice, non level-based damage or defense bonuses, and feats at 1, 3, 6, 9, etc. instead of every odd-numbered level. Instead of six skills and five feats, like PCs, they'll probably start with four and four, as well, giving them enough to cover one specialty but not giving them the breadth of ability of a starting PC.
As for experience points, I'm still working on that one. I was thinking of doing something similar to the HERO System, which gives 1 XP per session, plus 1 XP for good roleplaying, 1 XP for a particularly successful adventure, and so on, and then having characters level-up every 10 XP. That would completely divorce the stats of the nasties they encounter from the XP they receive, and emphasize the story and RP aspects. Alternatively, I might use the regular XP chart and simply break it down by plot point. "I want them to get roughly a third of the way to 2nd level in this adventure, which means each character has to earn 500 XP. So for the scene in the morgue, they'll get 100 XP each; for the scene in the speakeasy, they'll get 200 XP each and a 50 XP bonus each if they find the Yellow Sign behind the bar; and for the encounter with the gibbering thing in the outhouse, each survivor will get 300 XP..." I'm not sure about that yet.