This is my personal opinion . . .
I don't think POP proper is a good place for nightlife for a tourist couple. However, if you want to dabble, on the Malecon (beach front road in Puerto Plata) there are 2 places you can go to ,
1) is close to the Castle on the edge of the port, there is a reseraunt there near a disc called the Sphinx (you can tell the place by the decor). Nice place by the ocean to have a meal and see some of the locals.
2) on the other end of the Malecon is a reseraunt called Agua Ciro , this is a nice place also to have an afternoon meal.
This will get you the idea about what POP is like, if your at place #1 on Saterday, there is generally a tailgate party of dominican youth there (on-going affair). And a number of food kiosks are set up along the beach to cater to the party.
In general the All Inclusive resort has clubs and is the best place to start.
I'f you like I might be able to set you up with some one trustworthy that can show you around town. Best way to be social is to get to know a family in the area. If your interested, PM me.
-Lee