To chime in about the Sibelius issue, I'm coming to Sibelius-->ESX from Sibelius-->Kontakt, which I've been using for 8-9 months with good success. I understand and share some of your frustrations, but here are some obvservations, for what they're worth.
First, I've been very happy with the Sibelius-->Kontakt setup I've developed. It took a while to understand and create a setup that allowed the two programs to speak to one another transparently, so that, at this point, I never fuss with Kontakt once I'm set for a piece. (Oh, I rarely decide to add or adjust some aspect of the samples, etc.) It it a real trick to learn and implement everything, but once you're set, I have no complaints about how well it all works. I'm switching to Logic/EXS for two main reasons: the lure of potentially more available samples at one time, some of the parameter options/capabilities of the EXS, and the fact that upper level VSL is native for EXS. Later, I expect to also use other functions of Logic, but not the Score function. Don't get me wrong, for what it does, the Score part of Logic is great. It's just not Sibelius, which is clearly superior at notation...it should be, that's what it is. (By the way, I only work on paper or directly in Sibelius. I worked only on paper until 2000, when I did my second symphony directly in Finale, which I have 20 years experience using. From that background, I can tell you that I simply love working in Sibelius compared to Finale.)
As for various issues in Sibelius, I have them, too, but I've found a few ways to streamline the problems. Some examples:
1) I use macros to program my computer keyboard function keys (and other key combinations) with various often used tasks. I use a program called Quickkeys, but there are others. For example, Function Key 1 opens the zoom tool (glad to see that's now available in Sibelius 4, as well as the ability to program various shortcut keys). Function Key 2 opens the cresc./dim. plugin. (I could, in fact, program several specific operations with that plugin if I wished...several levels of volume change that might work for a variety of settings. I haven't done this, but it would not be hard to do.) Another function key is set to open the Live Velocity options window, where you can add, subtract, or scale velocities of groups of notes. You can even do this for an entire vertical stack of staves at once....not having to repeat this for each staff. If you have a staff you want to leave out of your vertical selection, simply Command-click it, and it becomes unselected without de-selecting anything else.
2) As for getting around the lack of an undo, here's one idea that can avoid copying backups of whatever you're fussing with dynamically. Setup your Advanced Filter to filter only Control Change 7 (or 11, if you're using that for volume). Select the passage you want to redo the volume on, filter it, and delete the CC data. Redo until you're happy. With experience, you become pretty good at guessing what numbers to use, based on the velocity of the passage. You can also fine-tune using velocity if you get fairly close. It's not a bad idea to make a chart of the mapping between Sibelius' 0-100% numbers and the 1-127 midi numbers. It's really silly for Sibelius not to include an option to switch between these two scales, but it's also fairly easy to live with this until they fix that.
3) Once you have the cresc/dim like you want it, you can use the Advanced Filter to copy it and paste it to other instruments...all at once, as many staves as you wish...even non-contiguous ones.
4) As for changing articulations, you can again use the filter function to copy and paste these wherever you wish. Remember that copying something in Sibelius is simply a matter of selecting it and Option-clicking in the spot where you want it...whatever IT is. For ex-Finale users, this one trick alone is amazing. You can also rubber-band select items or Command-select for noncontiguous items.
5) Also, don't forget the Live Velocity bars above the notes. If you turn this on, you essentially have Hyper-editing for velocty right above the notes. You can drag a velocity curve right there.
Sure, I've got complaints about Sibelius. Who doesn't? But I'll NEVER use Finale again unless it's to work with my composition students' files or to edit my old pieces. When I'm finished with a piece having done it in Sibelius, I'm done, and with an amazingly small amount of very quick cleanup, I'm ready to print.
Hope this helps or spurs more ideas. Now I have a question for everyone about hard drives, which I'm about to post in a different thread, and I welcome any advice.
Cheers,
Blind Lemon