I have the Stay on Target book and I really like the rules and the idea for using mounts included in that book. I also like to have a reason for walkers and other crawler ground vehicles. In my games I have adopted the idea that landspeeders and speeder bikes have some limitations as far as terrain. Speeder Bikes are a bit more forgiving, but landspeeders have difficulty with any uneven or extremely rocky terrain.

• Any significant slope that you cant speed up using momentum is an obstacle for a landspeeder. This includes inclines and also off-camber situations. The landspeeders slide around and are generally uncontrollable. Short tricks using the repulsor controls are possible but these require a check usually.
• Tall Vegetation, Surf, or large rocks (say .6 meters or so) will likely prevent a landspeeder from traversing the terrain.

Talents that help with terrain by ignoring setback can certainly help in these situations but there are limits to what the vehicle can do.

By comparison Airspeeders/Swoops have none of these issues except in trying to land possibly if terrain is bad. This also makes mounts and walkers/crawlers useful for very rough terrain.

Do you treat landspeeders similarly? Basically a bit like a normal car in our world?

May take:

Terrain is terrain, you don't get a free pass just because you float, if it's not a parking lot, you still gotta make a check because there's always that one feature you might misjudge. The thing about speeders though is that some terrains can be entered and other can't (or are so hard to enter it can't really be done in combat).

1)A speeder's max altitude is the determining factor. This allows certain speeders to be more useful in certain locations than others.

• The Aratech 74-Z, as a military speederbike has a nice high altitude of 25 meters (just don't fall off!) because it's an "all terrain" speeder, able to easily fly over rough terrain large rocks, bushes, ect.
• A Trast A-A5 with it's 3 Meter altitude is a good middle-ground speeder, able to go "most" places, but still limited to places with obstacles under about 1 story tall. (and still otherwise limited by it's hugeness as well of course.) Typically the A-A5 will only go that high to do things like shuffle around in a tight parking area, or the like.
• An X-34 with it's pathetic 1 meter altitude is really more of a "city" speeder, though in a "flat" location like Lothal or Tatooine it'll still work ok, as long as you stay out of places with lots of brush, boulders, or other small vertical features exceeding 1 meter in height.

2) Speeders can still "bottom out."

• The altitude is just a rough number compared to the ground on average. So wildly variable terrain will cause you problems. So like a field of small 2 meter deep craters will count the ground as being 1-2 meters lower than it may appear. Likewise boulders, bushes, trees, and buildings typically don't count as "ground" and are largely ignored.
• Likewise Ditches, trenches and so on can be "jumped" but not parked over, and larger features like arroyos will require you to go down into them, possible causing further issues if it's an especially steep incline. This is why "all terrain" speeders have such high altitudes, not to cruise at said altitudes as much as to allow sudden changes in the terrain below to be handled more smoothly.
• I pretty much agree with you about steep inclines. A speeder with a high altitude can work it, but a lower altitude one will "bottom out" before it makes the climb.

3) Water is not quite "the ground."

• Landspeeders (and bikes) have trouble over water. You can "skip" a landspeeder across a lake or river effectively enough (so like a chase that goes off the bridge can keep going, at least for a few rounds) but trying to maintain altitude for any length of time is futile (so no taking your landspeeder out to sea).
• Exception is speeders specifically built for traversing water, adapted to do so, and airspeeders/swoops whose repulsors are so powerful it's no nevermind.
• Extremely muddy terrain may count as water or otherwise affect max altitude, at GMs discretion. (rule of thumb: if you can [more or less] walk on it, it's ground. If you sink waist deep or deeper and have to trudge through, it's probably water)
• It takes a reasonable amount of water to cause this effect, no crashing cause you drove over a puddle.

4) Why Walkers?

• Heavy: Typically you'll see walkers have a specific purpose that makes a repulsor problematic. Walkers are usually heavier, or mount heavier equipment or weapons. To carry that weight legs and an engine are more efficient.
• Precise and steadfast: Walkers don't float or drift any, so getting into tight quarters and operating a drill makes more sense.
• Armored: Walkers tend to be a lot more likely to have an Armor rating of 3 or better. Not only is this part of the weight point, but having legs means you can armor them, making even the "weak" joints pretty resilient.
• No intakes: Speeders tend to be powered by jet turbines of one type or another. While mounting these on the top of the speeder helps prevent you from accidently taking rocks and debris inside, it's not a sure thing. Walkers don't have this issue, and so can navigate dense brush and rocky terrain without worry that a stray branch or pebble will blow an engine.
• Bushes and wires are for chumps: A Speeder gets into a bushy area. It has to slow down as it plows through them. A walker, being bigger and heavier is more likely to just be able to just brute force it's way through. Likewise heavy wires (be it features like a power line, or an obstacle intentionally placed on a battle field) can be pretty devastating to fast moving speeder. While walkers aren't immune to tripping, foot mounted wire cutters help a lot.