Question: Is it generally better to have a small number of fully upgraded rooms? Or have a larger number of not-so-upgraded ones? (Provided of course, that we have Power to spare.)

Wondering if the massive costs for upgrading are worth it. For example, I had a dweller training in a level 2 Strength Center with 2.00 hours to go. Then paid 4500 to upgrade it. The remaining time just went down by about 10 minutes! This seems pretty crazy since I could have built another 3-4 rooms with this cash.

Answer: 
Just to put some numbers here: 

```
Strength Level | Base    | 1st Upgrade | 2nd Upgrade
----------------------------------------------------
1 >>> 2        | 26m     | 25m         | 24m 
2 >>> 3        | 1h 20m  | 1h 16m      | 1h 13m
3 >>> 4        | 2h 40m  | 2h 32m      | 2h 26m
4 >>> 5        | 4h 27m  | 4h 14m      | 4h 3m
5 >>> 6        | 6h 41m  | 6h 22m      | 6h 5m
6 >>> 7        | 9h 21m  | 8h 55m      | 8h 31m
7 >>> 8        | 12h 28m | 11h 53m     | 11h 21m
8 >>> 9        | 16h 2m  | 15h 17m     | 14h 36m
9 >>> 10       | 20h 3m  | 19h 6m      | 18h 15m

```

Source: <http://www.ign.com/wikis/fallout-shelter/Weight_Room>. Other rooms have very similar (though not identical) numbers.

So you should be really only updating those if you have some ungodly amount of CAPS and it's burning a hole in your vault.

### Update

I have some 700k caps now, and I really don't know what to spend them on. Perhaps, now might be the time to upgrade some training rooms. However, more than half of my dwellers have full SPECIAL now and training rooms are half-filled, at best. Again, upgrading training rooms wouldn't have any effect, other than making me 50-100k caps lighter.
Later on, with large vaults, I'd say time is more important than money, and every little bit helps and are well worth upgrading the training rooms. Especially once you realize that having a Dweller's Endurance maxed out BEFORE they start leveling up drastically increases their hit points and start trying to max out level 1 dwellers before sending them to any tasks. At that point, the wait can get painful. 

That being said, from what I've been able to find, it seems like the # of dwellers in a room training at the time may have a larger effect than the level of the room. 

I haven't been able to find any greatly detailed or thoroughly researched numbers, but based on [this reddit post and accompanying spreadsheet](https://www.reddit.com/r/foshelter/comments/3auqxd/fallout_shelter_approximate_training_times_for/) going from stat 9 to 10 in a tier1 room vs tier3 room is only a savings of 1 hour 18 minutes. Whereas having a tier 2 room with 6 dwellers in it vs just 1 dweller going from 9 to 10 is a savings of just shy of 2 hours. 

So, it may be more beneficial to build 3 block training rooms and try to have 6 dwellers training at once, vs paying for all the upgrades. Of course, having 3 wide, fully upgraded training rooms with 6 dwellers training is going to give you the shortest training times possible.