It could be both. 1st and 2nd aren't very tall gears, and you don't move extremely fast in 1st, and there isn't a whole lotta speed (rolling momentum) going from 1st to 2nd. If the shifter is out of adjustment you may not get the required amount of rotational movement out of the shift shaft to shift gears. When the bike is rolling at higher speeds, it is easier to shift, because the trans gets "rocked" into gear by the turning speed of the front sprocket. Basically everything lines up and meshes together. Kinda like when you shift through the gears when the engine is off; you need to roll the bike while working the shifter to get it to "click" into all the gear ranges.
When cluthes go bad, they mostly slip, especially under load. Difficult shifting (hard to get or out of gears) tends to happend when the clutch wont release fully, which is called dragging(happens a lot when a slave cyl is leaking in cars/trucks). Now, if a clutch's friction plates are worn down to near nothing (but isn't slipping), the stack height (clutch thickness in a car/truck) is so short (thin in car/truck) that the clutch arm (fork or slave cylinder in car/truck) doesn't not have enough throw/movent left in it to completely disengage the clutch to allow for gear shifts.
So, it could be either or, or combination of the two.
If it were mine, and it didn't slip any, I would ditch the shifter linkage, adjust the clutch cable and take it for a good ride to see how it does. The stock shifter sucks monkey nuts, so you've already eliminated a headache area. If it is still giving fits after that, then I would replace it. The driveline is a noice clutch, and VERY affordable. All total you'll have around $70 bucks in the clutch kit and clutch cover gasket. For that price, you might as well do it, and know it is good to go. But, I was in a teaching mood this evening. lol
