The Meaning of Life, the Universe, and Everything.
I have the same problem. I usually entertain myself with mini games on servers, like prison, factions, creative, survival... I would recommend a server called The Chunk. It has a variety of cool mini games, such as Death Drop, Tower Defense & more! Yes, playing with mods is much better than vanilla minecraft. Maybe you should consider making your own server. Or try creating new mini games using mods. Or... start recording! Record seed showcases, mods showcases, let's plays on single player or multiplayer. This can really entertain you in ways you cannot even imagine! Or at least that's just me.
Find a village and just destroy it with fires and TNT. Or you can just move to a different area and start from scratch with all the materials you already have! That would keep you up and you won't get bored at all.
Take as much as you can carry and go explore. Since you've already done this maybe go to the coolest place you can remember and set up a whole new base there. Then connect it with underground tunnels to you old base or maybe just a gravel path on the surface. Then go somewhere else and make another one. build entire kingdoms...that are completely abandoned xD maybe put some villagers in there.
b l o w t h e w h o l e t h i n g t o b i t s a n d s t a r t o v e r
For real! Just either gather as much as your being can possibly handle and blow it all up and start from the ashes, or just start a new world. Whichever of these you do, try to make everything 2-3 the scale as before!