The biggest predictor of a society's average predicted lifespan is infant mortality. Most of the gains in average lifespan over the last 100 years is from increasing the number of children who live past 2.
3 years increase from a non-infant mortality related improvement is actually pretty huge. I'd have to look it up, but I think the impact of non-infant vaccinations would be roughly a similar sized increase.
3 years increase from a non-infant mortality is pretty huge only when compared to what we have done before - but it's not huge compared to the actual lifespan.
Going from 80 to 83 (for example) is nice, but it doesn't have a radical impact on how we should live our lives - going from 80 to 160 could do that. If we want major improvements, then we either need to make sure that the other things are cumulative (say, that we can get 20 disease-cures to add 3 years each); or we need to look in completely different directions.
It depends on what you see as a goal - in the long run, I believe that we can get to lifespans measured in centuries, because it's technically possible as seen from other lifeforms. If the marginal improvements due to curing diseases can't get us there, then we should investigate other options how to achieve that, instead of treating a 5% increase as "pretty huge" and being satisfied with that.
3 years increase from a non-infant mortality related improvement is actually pretty huge. I'd have to look it up, but I think the impact of non-infant vaccinations would be roughly a similar sized increase.