The caffeine pill might have increased the way that you perceived the effects of the Vyvanese and certainly increased the overall stimulant effects on your body and mind. I have a prescription for Adderall, which is quite similar in many ways. Never took Vyvanese, but I take Adderall often as I have a prescription for it. Amphetamine-type stimulants definitely cause some euphoria, and they do seem to make music more interesting for me anyways as well. When I have combined my prescription amphetamines with caffeine, I have found that the effect was increased. For me, this type of increase in the effects wasn't enjoyable as caffeine creates a jittery effect and generally bad feeling for me. Though, it definitely can increase the effects and for some, the combo could undoubtedly make the buzz better for them. The fact that you were off it is another major factor though. Your tolerance has more or less been "reset" by your week off, and your Vyvanese is hitting you harder than it usually does because you don't have the tolerance. That likely is another contributing factor to why you feel the effects so much more. I find that my addies have a substantially stronger effect on me as well when I take some days off them.
For some reason, I have gotten in the pattern of taking them every day. When I did, even taking a higher dose did not do much to increase the effects in any meaningful way really. It increased the effects, but it wasn't really that worthwhile. If you take them every day with no days off, you build a tolerance. Recently, I have taken a few days without them, and I have functioned fine...... as fine as I did before meds. And then after taking them, it has given me a boost and enhanced my productivity to more than it was before I took prescribed amphetamines. When I took them every day, I lost the increase in productivity. On days that I took them, I was no more productive than I would be otherwise. But I got in the pattern of "take the pills" every morning. So, definitely now that you took the pill without having taken it for a week, it would have a stronger effect. In fact, due to what I realized, I have realized that it's better to take them a few days a week (5 days a week if you have a 9 to 5, if you're self employed then perhaps up to you), but at least two days off a week is a must. My doc said this to me before, but since it said on the bottle take one every morning I didn't really take days off of it.