The tank would be a nice size for a number of setups I have dreamed of over the years, including:
- A mbuna tank with 2 or 3 groups of 1m5+f haplochromine cichlids from Lake Malawi, Lake Victoria, or both
- A tanganyikan community with several species of cichlids from that lake
- A paradise fish biotope with two pairs of paradise fish, a large school of white clouds, and about 8-10 golden barbs (preferably the wild green variety if possible...it's arguably just as pretty as the namesake golden form).
- A lake inle biotope with large schools of sawbwa resplendens, danio erythromicron, Devario auropurpurea, or other species from that lake
...basically, there's a lot you can do with a 55 gallon.
About the aquarium: it might not hurt to re-seal it in the near future, just to reduce the small chance of a mishap occuring from the aquarium's age (the sealing wears out after a while).