There is one question I can guarantee someone will ask as I begin an engagement with a new client. It usually comes in the second half of the first major session I have, called the Agile Orientation. By that point in the initial training, we have covered the roles and components of Scrum, using it as the primary (and my favored) option for an effective Agile process in most businesses. The looks on at least a few faces at that point let me know that people are starting to process just how disparate their current work life is from what I am describing. One of the more outspoken folks usually asks something like this:
If Agile requires all these things, and we can only implement part of it, is it still worth doing?
The answer is yes, with one caveat. A partial adoption results in partial benefits, so expectations should be adjusted accordingly.
I think that's one thing that most groups adopting Agile miss. They acknowledge at the onset that they cannot or are not willing to implement several (often crucial) elements of Scrum, but they sill expect to be "just like the stories" they hear at conferences. But, of course, it doesn't end up being the utopia that either they envisioned or some hand-wavy, hands-off coach sold them.
The real foolishness comes when practitioners blame the process they never even managed to implement for their less-than-satisfactory results. I am seeing this disturbingly often of late. People are speaking ill of Scrum, and when you manage to get a bit of context out of them, it turns out they don't understand it, and their attempts to apply it verge on abominable. If all a group managed to do was have a daily status meeting where some or all folks were standing and have people commit to work in variable-length sprints, can they really be that surprised to not see much benefit?
Yes, Agile is still worth doing, even if you cannot do everything at once. Any improvement is worthwhile, even if the full potential is not realized. Just be sure that expectations are adjusted. Consider the following comparison from another area of life:
If you signed up for a 10k race, and the morning of the race you decided to walk rather than run it, should you really be surprised or disappointed if it takes you 6 times as long as the first 100 runners across the finish line?
There's a direct relationship between how fully you adopt Agile process and practices and the amount of impact or improvement within your group. When adopting Agile, it's not that your mileage may vary, it's that it will vary. Accept that, and you'll spare yourself a fair amount of self-inflicted disappointment.