Do what thou wilt shall be the whole of the Law.
First of all I'd like to add my recomendation for practicing Bach to the stream. When I was young I HATE HATE HATED
Bach!!! His music was so devoid of feeling and expression to me that I avoided playing his music as much as possible and instead spent all my time with Chopin and Prokofiev!
Decades later I began taking lessons again and my teacher (Dr. Beaudette) had me audition and would not let me play ANY romantic music at all. Instead it was Bach and Mozart
(as well as Debussy). At first I grudgingly went along with her plans, then after playing through Well Tempered Clavier one day it finally struck me as to just how much Bach had improved my technique. The way Bach makes you alter the way you THINK about music opens up a whole new world of performance technique, at least it did for me. Although I would HIGHLY recommend getting both books of WTC and playing through them thoroughly, I still would branch out into other pieces as well.
As for Czerny's School of Velocity, etc... For me personally I'm feeling my age in the speed of my fingers. Sometimes I sit at the piano to play and my fingers feel like rusted-over-molasses!!!
I've found however that a good 30 minutes to one hour of Czerny's School of Velocity gets my fingers pumping with blood again and they become much more spritely and fluid. Don't start off with so much though, after a great absence. Sometimes I'll sit down and play through Book I then take a half-hour break and come back and play through Book II and so forth. Czerny's musical ideas, I'll admit, were sometimes trite; but his techniques were remarkable. Remember when playing Czerny that the fingering for the pieces is THE most important aspect. Many times I'll have to slow an allegro down to Lentissimo just to play using Czerny's fingering but it pays off in the end. The important thing to remember when returning to playing after an absence is building up finger dexterity again is just body-building for your fingers. If you go too gung-ho, you'll have a greater risk of injury, so just take it slow at first until you've warmed up to killer workouts again.
With that out of the way, I'd like to make some other suggestions that others have overlooked as they all are excellent technique builders, and at the same time are beautiful music that's quite enjoyable to play.
First to gain the legato skills back, Chopin's Preludes and Field's Nocturnes are indispensable.
To work on refreshing control of dynamics and expression, get a copy of Debussy's Preludes, especially Book I. These all range from fairly easy to fairly insane, so you'll have to just play through until you find something that speaks to you.
To free up tonality and voicings, try Bartok's Microcosmos. Start with whichever book with which you feel comfortable. Chris Breemer may also have some good ideas concerning Bartok's repertoire, since he's recorded so much of Bartok. (Music for Children isn't just for children!!)
Lastly, the study of Scriabin should be included in every pianist's studies.
His etudes Op. 8, Op. 11, and Op. 42 while being some of his most popular are also EXCELLENT for building up hand-separation, as well as polyrhythmy. Take them slow and try to play them at first with a metronome until you get the rhythms down. The techniques you build will apply to EVERYTHING else!
Also as far as sight reading goes, try to play new music as often as possible. Get copies of Rachmaninoff's Etiudi Kartini Op. 33 and 39, Prokofiev's, von Beethoven's and Mozart's Piano Sonatas, pieces by Ravel and by Granados. Easier choices might be some of Grieg's pieces for children, Clementi's Sonatinas, etc. By forcing yourself to play music that's beyond your present abilities (whatever they happen to be) actually increases your abilities much more than playing the same songs over and over; and the more you do this the easier those difficult songs become.
Hopefully this has given you some ideas with which to work. The pieces that I've mentioned were all VERY instrumental in forcing me out of my Romantic era shell; and ALL of them focus upon a different developmental technique. Good luck! and Enjoy!
Love is the law, love under will.
P.S. If you're into other musical forms, don't forget John Mehegan's Jazz Improvisational Techniques.