Having visited Munnar twice, once from Kochi (Feb'14) with office batchmates and another time from B'luru (July'17) with school mates and it has been my top pick for a long weekend. (Usually, I visit places multiple times only if I like it). I hereby lay out my itinerary which helped in best experience of Munnar, if you cover most of the places mentioned below.
Night #0 (for Bangaloreans):
Start early on a Thursday night, to reach by Friday noon. As we were starting from Bangalore, via Salem and Dharmapuri to Munnar, we had to start early for this 10-12hr journey of 350kms.
If it was to be from Kochi - the 120 km distance can be covered in 5hrs on Day-1, if you started early in morning. And the below Bangalore itinerary would reverse on Day basis.
The low budget trip was through low rental stay and a good hatchback fitting the budget.
Day #1 :
On the way to Marayoor, 40-50kms prior to Munnar (should be covered between 9am-12pm, choice is yours 3:D) any of the below can be covered.
1.a (Chinnar Wildlife Sanctuary)
1.b Domlen sites of Marayoor
1.c Marayoor Sandalwood Forrests
If the above couldnt be seen, try to cover the below spots
Within 20kms of Munnar on the route from Bangalore: (Should be reached by 1pm, as 2.a/2.b spots close their bus rides by 3-4pm)
2.a Anamudi Peak (Need to take bus tickets separately) -
2.b Eravikulam National Park (Need to take bus tickets separately while covering 2.a)
2.c Lakkam Waterfalls. (~can be covered during return to Bangalore as well)
~~ Munnar, Hotel Night stay.
Look out for spa therapy nearby (on avg, 2k INR), and local dine outs.