Is there a noticeable difference in handling due to the added weight of steel wheels? (seems to be 5-10 lbs more per wheel, ignore the salt
and potholes for now) (scaling safety and performance)
Yes. Assuming that your steel wheels are heavier than your alloy wheels (which might or might not be true), you'll be facing an increase in unsprung weight and rotational intertia. Your handling will be somewhat affected and you won't be as quick to accelerate or to brake. More specifics are required for a complete analysis.
Are there safety concerns due to the potential bending of the steel
wheels or are minor impacts from pothole too minor to be a concern?
I.e.: During an accident, would the wheel type be a factor in the
amount of damage to the rest of the car parts? (scaling safety)
If you bend a wheel, it won't work as well. If you run into another car, it's unlikely that your wheel choice is going to matter: the frame, body and crumple sections dominate that situation.
Would winter and salt do more damage to steel or alloy wheels? In what
ways, quantify the amounts.
It depends. A steel wheel will rust wherever there isn't paint. An alloy wheel might be affected by salt to varying degrees. The specifics of the allow are required to decide how much of a protective oxidation layer might form.
What is the best long term value given that steel wheels may bend
while both types may get salt damage and require replacement/repairs?
It depends. Can you afford two sets of tires and two sets of wheels, allowing you to switch for winter and summer? That's the best bet. If not, are you willing to replace or tolerate bent and rusted wheels for a while before spending money on them? If not, steel wheels might not be for you.
Bonus question 1: Is there a noticeable difference in performance and
safety of lighter and higher performance alloy wheels compared to
standard ones. (E.g.: Enkei Performance or Tuning Series to unbranded
It depends on the driver, the vehicle and the environment. Are you on a track driving at speed? If not, it's going to be more difficult to perceive the difference. Are you driving in a rough road environment? If so, you should purchase more robust wheels or there will be tears when you break a hub.
Bonus question 2: Are there pre-treatments to steel wheels that would
help prolong its lifespan by reducing the occurrence of rust? Assuming
the steel wheels come painted.
Yes: paint and more paint. Keep the salt away from the metal and the metal will last longer.
What I do:
I live in a region that gets salted when it snows but we generally have fairly mild winters (barring the odd hurricane, nor'easter or blizzard). I'm still running with the stock allows that came with my car. If I had the cash, I'd pay for some nice summer wheels, get summer tires for them and keep snow tires on the stock alloys (but I don't so I won't). I've never even considered getting steel wheels.
Updated some years later:
Quite some time after this answer, I managed to put the cash together for another set of wheels and tires. What I do now is the other option: I use my aging stock alloys as the wheels for my winter tires (they haven't been pretty for a long time so winter grime doesn't make me sad) and I have a pretty set of wheels with dedicated summer tires.
Caveat: I almost never need the winter tires for serious snow. Climate change where I live has caused some significant differences in snowfall so it just doesn't get all that wintery around here. That said, my summer tires are terrifying in anything like slush, snow or ice. With the winters, I never have a concern and, when the rare deep snow does show up, I'm happily kicking up four rooster tails wherever I go.
However, mac is right: the winter tires do not have the dry grip that the summer tires do. They can't: the combination of tire compound (for lower temperatures) and tread block design (they have sipes to dig into the snow) means that they have less overall grip and, at the limit, things feel much more sketchy. However, I'm a Dad and I like having a vehicle that I know that I can count on to get me through a winter.
Note: I still don't have steel wheels and, if I did bend one of my ancient OEM wheels on one of our horrifying winter potholes, I wouldn't get any. I don't like the certainty of rust combined with the fact that I don't like their looks. I'd rather get a lower priced replacement alloy wheel (or set) and enjoy my car's winter shoes.