I've considered making this transition myself. I've built up a roll on a half-dozen sites, mostly from MTT play & SNG,
freerolls, private tourneys, etc. I've also read a bunch of other player's experiences with playing MTT & SNG and then making a transition over to NLHE FR & 6-Max and not one of them seemed to have regretted it (although maybe the others just didn't post about it?? lol).
As I'm sure you're aware of, there's tons of stuff to learn when playing the cash tables and also some habits picked up from SNG play that need to be dropped.
So... I gave it a go for awhile on a couple of sites and did okay with it.. BUT.. it never really grabbed me to the point of wanting to put in the necessary time I believe would be necessary to get very good and to move up in limits. Now MTT's on the other hand... my interest never seems to wane,... just wanting to soak it all up.
I strayed from playing cash tables but have occassionally put in a few sessions at micro limits (10 & 25NL). It's just never grabbed me up to this point although lately I've been considering making the move towards it again.
As far as 'mixing it up' goes... and always playing a variety.... I disagree with this personally. I find it much better to just focus on one type of the other... >> MTT's... SNG's... or CashTables. I get better results this way by far (even with SNG's... it's either 6-handed, 9-plyr. reg. speed, 6-plyr. Turbo, 9-plyr. Turbo, 45's, etc.,.... it's one or the other... I prefer to not play a variety. Focusing on one particular type/variation has been working better for me (when I first started out I'd switch around all the time) ).
Another cool advantage to playing the cash tables is that you can just sit down at any time for a short session. THis is great if one doesn't have a window of oppurtunity to make the time committment for an MTT.. or even SNG. I still prefer MTT's though... and will keep pasting notes on my door saying I'm not home.. I'm sleeping,... I'm sick...etc... ha ha ha.