looks like you've got some decent fretwear going on already.. hopefully its not notching yet
if the string height doesnt follow your radius you have one of two problems, the first being more likely.
1. your bridge saddle has notches in it from the guitar being restrung over the years (especially if its a plastic bridge saddle). the part you're looking for is the little white piece of plastic down near where your palm rests on the bridge. check to see if your thinner strings have dug themselves a little trench. if so, you can take it to a guitar shop and he will take care of it. or you can get a new bridge. if you get a new bridge, and if you care about the guitar enough, i would invest in a bone or sythetic bone material that is harder than plastic to prevent this problem in the future. if this is just some cheap acoustic, get a plastic one. or else you'll be spending unecessary money on a cheap guitar.
2. your string notches in the nut might not have been notched properly when the guitar was last setup. the nut is a piece of plastic up near the headstock at the end of the neck that keeps the strings in place and separates the speaking length of the string from the non speaking length. with this problem you can put a drop of dense modelling glue (one that is recommended for plastics, or else it will melt your nut, and nobody likes melted nuts
) and fill in the notch that is the problem, then take it to your guitar shop and have him reset the nut slot with a nut file so that it properly fits the radius (curvature) of the fretboard).
onto the first problem you mentioned, the distorted sounding notes near the top on the top two strings on relatively higher frets. before all else i would check and see if your highest fret isnt too high, if it is you can take it to your local shop and have him level it. or it could be either a loose brace, which is rather unlikely because they only vibrate sympathetic to lower strings and notes, or you have a really loose trussrod that is broken and vibrating sympathetically with the strings. ive seen it on 2 acoustics that entered my "shop" if you can call it that. if this is the case theres really not much you can do. with acoustics you cant just swap out a neck. you have to go through to nerveracking process of breaking the finish around the neck joint, heating up the glue and separating the neck..
you could also check your tuning machine mounting nuts and see if they are loose. if they are, only tighten them till hand tightened then give about an 1/8 of a turn with a wrench or pliers, being careful not to damage it.
theres some other things i can think of but i would check these first before we get into depth with this one..