I have learned my way thru 5 to MC7....my current daw and have at times wondered if I should take the Sonar plunge. But I usually just slow myself down and realize MC7 is taking care of all my needs for recording with plenty of plugin capability (of which I use plenty)as I still learn and practice as I write/record/mix.
I find MC7 is reliable and consistent and I don't think its a reasonable move for me at this time to begin to have to learn all the nuances/diff's between MC7 and Sonar (though i suspect i would figure most steps similar...).....ie it will slow my current workflow. I do wonder at moments if Sonar would afford more efficiencies in the long run ...though surely I wouldn't really know personally unless I cross that bridge to begin learning its curves and locations of needed things.
That said.... I guess it really comes down to your personal goals with it. If MC7 is getting your recording/mixing needs met...likely no need to switch trains. The Sonar train is enticing....but I am happy on my current track/journey and views ;o) Good luck....I do look forward to that new rail system someday...but my main goal/focus is the music at this time and MC7 is rolling along well with me.
ps....love to hear from ya if ya do jump to Sonar and share what ya liked better (hopefully lots ;o) )
EDIT: I meant to add....at this time also....I don't think Sonar would give me any better "Recording" results vs MC7 ....so that right there does not warrant a "need" to slow my flow and switch . I am EXTREMELY happy with the results I am getting. I am recording with my drumming pal and will be bringing more players together...band intentions....as we write/record originals and covers.