Do all of you use the clutch to shift up/down? Is it absolutely necessary to use the clutch all the time? If so, what kind of wear will occur by not using the clutch? I've heard that by "blipping" the throttle, you can upshift and downshift without using the clutch. Is this true?
Years ago I had a grip-change Lambretta and often changed in the manner you describe, up was OK, down sometimes iffy, bike was shaft drive and very forgiving. Now I've grown up i tend to think "What's the point?" but you probably could do it.
Blip the throttle to match engine/trans speed and kick it up. You'll pick it up quick and if you're not grinding you're not doing damage. Downshifts are a bit trickier. I almost always clutch down, but only clutch up when riding casually.
How do you match the engine to the trans speed? Trial and Error?
Preload the shifter with your toe. When you let off the throttle and the rpms drop, it'll shift as soon as the gears match up.
On more casual rides you should still preload the shifter - you'll only need half the clutch.
You'll feel it. Upshifts are easy to get used to - just get out of the throttle a split second before you shift. You really just need to take the tension off the gears long enough to engage. Matching engine speed is more critical on the downshifts - even with the clutch. Blipping the throttle on downshift will make for smoother transitions once you get the hang of it.