划算 vs 值得

1. 划算 is usually related to spending money. If you make a cost-effective purchase, that is 划算.

Say for example, suppose you pay the same money but get double quantity of goods / service with the same quality, that is a good deal. 很划算.


2. 值得: be worth; deserve. 

When it's not related to calculating the money of cost, we can't use 划算 instead of 值得. 
e.g.
考试通过了，值得庆祝。（can not say：考试通过了，划算庆祝）
We have passed the exam, it's worth celebrating.