Extending a 5 point ordinal scale to 9 points while maintaining comparability We have a lot of data regarding a 5 point ordinal scale with descriptors for each point like 'very little' to 'very much'.  I am worried that this scale will show insufficient variance in a further study I am designing, and would like to extend it in some way which a) captures meaningful information but b) maintains maximum comparability to the previous data.

Options under consideration:
1 - add blank items in between each of the old items on the horizontal row, rely on individuals to interpolate.
2 - invent new labels which somehow fit in between the old.  This may be linguistically challenging.
3 - convert to a numeric scale with comparably labeled beginning, mid, and endpoints
4- convert to a numeric scale using the old labels at every appropriate point, and blanks otherwise.

Adding additional questions to capture the variance is not an option, but I'm interested in any others I haven't thought of, and for and against arguments.
See this question on comparing scales with different response scales. In short, you have to do it with care. A good option for ensuring comparability is to get a sample of participants to provide responses on both response scales in order to see how they relate. This could then be used to create a conversion scale. 

More generally, there is a large debate about the optimal number of response options on traditional survey items. In particular, if you are more interested in means of groups rather than individual-level measurement or if you have multiple items that are aggregated, then the move from a 5 to a 7 or 9-point scale is not going result in much more differentiation. It can be good to think about how well and how consistently your participants interpret the meaning of the scale. Adding points would increase the variance, but a question remains about whether it reflects variance in the true score of interest, or whether it reflects rating bias or something else. 

Personally, if comparison with previous research is important, I'd generally leave the rating options as they were.