I was just using beginner examples to convey what I think, since everybody can understand what it represents, didn't mean to judge of your level
I think it still stands valid even at "higher level", though if you really find yourself incapable to sight-read decently there might be something else troubling you ; I know I have horrible pitch recognition despite my best efforts (I mean really horrible, anything that is not played on piano I can hardly even get the most basic melody), so I guess one could have the same fault in sight-reading.
Also, sight-reading is really dependent on what music you are used to play ; someone who plays a lot of Bach would have troubles sight-reading Scriabin for the first time I guess. In the same way, not every music asks the same of the sight-reader ; some have many modulations and accidentals, some have huge chord clusters, some just have huge chords, some have complex polyrythms, etc. So I think evaluating what kind of music you want to sight read (at first) is a good start, so you'll know what are your specific weakness ; I guess you have no problem reading individual notes on the staves (plenty of flash minigames on the net, I think Juufa linked one somewhere, that are really great for that. I learnt a fair part of Japanese writing that way, really fast), so there must be something else. Sight-reading requires a bit of memorizing too, being able to look forward and remember during easy passages so you can prepare ahead, remembering chords and how they looked like on the sheet (so you don't have to read them whole again, in a way tying the hand form to the sheet drawing). Maybe you could simplify the sheet you want to sight-read first, maybe use jazz notation for some chords if you're familiar with it ; many complex looking chords that are hard to decypher have simple names and can easily be played. When there's many voices in a piece, I try to sing them first, or even play them separatly and modulate them on the keyboard first.
I'm no great pianist, but the otherday I was sight reading through Prokovief's Montagues and Capulets for fun, and the first thing that came to mind glancing at the sheet was "that beginning is just like an alberti bass (with chords) with rocket start (you know like in that first Beethoven F sonata), and it made the whole playing much easier (I could focus on other details and on the following section). Apart from that, you mentionned hard pieces - usually, when there are technical difficulties, I sight read the easy parts, and just memorize the hard parts ; trying to sight read hard parts will make it harder to learn the piece, as you will slow down on both your playthrough and technique acquisition, eventually not ever playing it correctly and - worse - learning it wrong in your hand memory. I've always wondered if virtuosos can just take any sheet and play it ; like you know, "Scriabin 10th sonata ? Never heard, I'll sight read it", and bam they do it right there. I know some people have great ears, so they have a good part of the sheet memorized before seing it too, that might help...
So, what pieces are you trying to sight-read ? Could you learn them easily (note wise mostly) if you wanted ?