The situation you drive is almost identical too what I do every day. I have OEM steel wheels with smooth wheel covers and I coast 1-1.2 miles a lot
As for LRR, I just put a set on my car and noticed a 5-10% improvement in FE. If you plan on getting some just find the cheapest set of rims you can, lighter is better but only if they are in the same range. I went to my local discount tire and explained what I wanted and that I was going to drill and tap them for smooth covers and the manager said he would watch out for a set. I was looking for some winter tires and asking in August, so I expected to wait a month or so. three weeks later he had a set,of OEM aluminum, slightly scraped up but not bad and gave me a discount on them which brought the price to the same at steel wheels. right now they are on my winter ties.