Research paper about an enhancement to algorithm
The question I would ask is: "Are there people working in this area who would learn something interesting and useful from what you've done?"  If the answer is yes then your paper makes a contribution and so is potentially publishable. At that point you could consider some secondary questions, e.g.:


Length of the paper: this should be commensurate with the extent of the contribution (i.e., how much someone would learn) -- a small contribution merits a short paper.
Venue of publication: some place (conference, journal, forum) typically accessed by the people who would learn the most from your paper.  For example, a theory journal would not be the right place for systems-oriented paper about the guts of a compiler.