I don't think there is any spin going on here. The study's result was that Clearview does not show a "statistically significant" improvement over FHWA Series in terms of legibility. It seems that they are about on par, or that Clearview is better in some situations and worse in others. In the study, it seemed like people had some problems with the Clearview numerals in particular.
Which glyphs, in particular, do you feel "need to be fixed"? I have heard from several people that the FHWA fonts are "clunky" or "outdated/less modern" or "ugly", but I've never really heard specifics as to why they feel that way. I will agree that on most series, the lowercase "w" is ghastly, but that's the only character in particular I have noticed as being particularly ugly. It should be noted that while the uppercase characters were designed back in the 1940s, for all series other than E(M), the lower-case letters were designed much more recently (I want to say 2000 or so). I understand that "modern" fonts usually incorporate variance in stroke width as Clearview does, but I would guess that a consistent stroke width is more legible.
As mentioned before, vanilla Series E glyphs contain larger counter spaces than E(M), so you might consider how Series E fares in the Gaussian blur tests if you haven't already.
I agree that the most pressing need in sign improvement is not to the typeface, but rather to the actual design of the sign. A lot of signs, especially in Oklahoma, appear to be drawn up by someone who is ignorant of the basic tenets of design. Some states are better at this—take a trip on a KDOT-maintained freeway (i.e. not the Turnpike), and it's hard to believe that they're even following the same manual as ODOT.
With regard to I/l from above—in FHWA Series, lowercase l has a slanted top, while uppercase I does not. So "Illinois" and "IIIinois" and "lllinois" would look different.
