I won't belabor the point about interpreting images any more. I was having that conversation as much with myself as with anybody else, to try and keep my own enthusiasms in check.

Fossils may be statistically rare, but there's nothing like marine sedimentation to concentrate them. And of course the frequency of fossils is inversely related to size (as it is with living organisms). There are limestone beds on Earth which are composed mainly of fossilized remains of the hard parts of ancient microorganisms. Whether we find microfossils would depend a lot on whether (hypothetical) Martian life got as far as multicelluar organization and creation of hard shells and other durable structures. If it didn't, we might still find impressions left by soft-bodied organisms in the dirt, but those would be rare.

Rocks can contain signs of life other than fossils. During the water press confference, somebody theorized that the blue spherules were formed by tiny specks of iron embedded in rock interacting chemically with the matrix, suffusing iron compounds outward symmetrically to form the spherules. That explains the formation of them forward in time, but then I have to wonder where the iron particles came from. There could be lots of nonbiological explanations, but it's also possible that the iron particles were left behind by iron-concentrating microorganisms. One reference to terrestrial iron-concentrating bacteria I found went so far as to flatly say "Sea life, in the form of ancient iron-concentrating bacteria, has also created the deposits of iron that we mine." Undoubtedly too sweeping a statement, but intriguing nevertheless.

One door closes, another opens. Wet Mars forecloses some possibilities, allows speculating about many more.