I'm not 100% sure what Toyota calls the vertical underfloor spoilers ahead of the tires, but the front ones are:
Part #:
LH 53852-02120
RH 53851-02140
They can be had for roughly $25. And yes, they help reduce drag and thus increase your fuel MPG. They do this by routing the air around the tires instead of letting it plough directly into them, reducing the high pressure wake build up ahead of the tire.
The LE has these panels (circled below), just not the front undertray or the middle underfloor (I do know Toyota calls these "under covers") panels. And yes, Toyota indicates a .28 cd for the LE Eco, which comes via the entire set of underfloor panels plus the spoiler. Contrary to popular opinion, spoilers can actually induce drag reduction as they create a sharper separation edge, enhancing the turbulent kinetic energy into the base area flow. Yes, if you crank a spoiler up with positive angle it will indeed induce downforce as well as a ton of drag, but the spoiler you typically see on EVs and fuel sippers is a different beast and performs a different function.
The standard Corolla has a .29 cd, so the entire kit produces a .01 reduction in drag. While it doesn't sound like much, that it's bolt on should be enough encouragement to pursue if interested in fuel MPG increases. I've currently added the front undertray ("splash shield" in Toyota nomenclature) to my LE as well as the spoiler for a total cost of around $80 about a year ago. Just recently saw the front undertray for $25 (I paid $40) and aftermarket spoilers can be had on eBay for cheap. Just insure you're ordering something that's a faithful mimic to the Toyota version (i.e., effectively flat in angle) and not one designed to produce downforce. The issue then becomes adding the 4 middle panels as Toyota wants roughly $100 per. So for now I haven't done that. I have the skills to make my own using rigid foam insulation with fiberglass laid up over, but it's a matter of finding the time. Had hoped to find a wrecked LE Eco and pilfering off of them, but so far I haven't had much luck (though in fairness I haven't been too actively pursuing, that being said, I've never see an LE Eco in the flesh on the road; do they even exist, lol?).
Anyway, tweaking the aero of my LE is an interest of mine and I've done some very small items here and there, mostly looking at panel sealing and radiator inlet infill panels; low hanging fruit as they say. Have they produced results? Hard for me to say, I'm not an A-B-A type tester and my work route is pure city (In years past I've had glorious hour long commutes and indeed you'd see the cream rise to the top over time on the spreadsheet on these long daily hwy trips). I'd love to be more aggressive and look at a full underfloor, but that's not the easiest of tasks and takes some consideration in order to make a durable and safe part.
Anyhow, realizing I've just hijacked an ages old thread to wax on about the esoteric. Apologies!