Here is some info on other Villages and Towns that unified and their experiences.  Every situation is different:

• Seneca Falls - Voted for unification in 2011.  The Center for Government Research normally estimates savings in the range of 3-10%.  This article reported a larger decrease for former village residents due to increased income for a landfill based in the town.   A complete story by the Democrat & Chronicle.
• Randolph – Voted for unification in 2011.   The village government was pro-unification and the savings it would bring.  The combined community size now is about 5,000 people and they saw about a 10% tax savings.
• Perrysburg – Voted for unification in 2011, saved about 13%.
• Johnson City, NY:  15,535 residents.  Great academic review for future dissolutions.
• Village of Edwards plan:
• Village of Malone, NY
• Altmar:
• Hoosick Falls:  Just consolidating won’t save money, dissolution will.