if you invest in energy, it typically means less that you invest in vitality, leaving you with lower life. Late in the game, every little bit of life you have will be appreciated, and since late-game is where most people "hang out", guides take that into account. Also taking into account that late-game is what most sorcs have for a goal, then points you spend in Energy now will be "wasted" later (when your mana can regenerate itself sufficiently without any points you've spent).
However, boosting your energy to ~75 isn't likely to "break" your build though, but I wouldn't spend any more points than that.
The biggest help right now will be to focus on items that add +mana: Perfect Sapphires socketed in armours and helms is a great start. Tir runes (+2 mana per kill) in weapons and shields is also a good helper. A few items are very cheap to trade for too (Frostburn gloves and Manald Heal rings are two good ones. And you can always make Insight in a normal polearm - I have an Insight Halberd that I use for that purpose - and stick that on a merc to give you insane mana regeneration).
PS. Depending on your build, equipment, and skills you're using, then your mana should start sufficiently self-replenishing somewhere between level 60+ and never.
4 socket voulge drops often enough, though you have to be in NM act 2 or later (or was it act 3) to get them to start dropping. If you are playing untwinked and have no character that can run those areas, just stick some points into energy.
If you're non-ladder. Stick with those ideas above. + mana per kill is good if your spells do enough damage to mass kill. A 3 socket shield with a mix of Tir runes can be a good option if you don't need the resists. If you do combine them with diamonds. Wall Of The Eyless give +5 per kill, Lidless Wall gives 3-5. Both give 20 FCR also wich is good for sorcs. Collect all mana charms you can. Then, there's always mana pots. When I played Classic sorcs I used to reserve 2 rows of my belt for blue potions.
Yeah insight is an option if your merc allows it.
Some builds allow you to put points in warmth as well.
However, if i got to choose between putting points in warmth or energy, i'd put some points in energy. Complaints from high level sorcs about not having enough mana are not at all uncommon. Energy is typically underappreciated, and rightfully so in a lot of cases, but I think your sorc can really benefit from 50-80 points spent on energy. If I didnt have CTA, I'd be low on mana all the time to be honest.
I also don't think it matters much whether your life is 100 hitpoints higher or lower, seeing as even a few perfect rubies could make up for that bottleneck if it was one.
I do advise you to keep strength as low as possible, because it is there where the sorc can really waste attribute points, imo.
A lot on this issue also depends on the equipment you use. 2x Spirit + frostburn + shako = plenty of mana for mid-level spells. Silkweaves, as mentioned, are a very nice form of mana leech. Silkweave + lidless wall = 10 mana after each kill...
Lastly, do consider mana pots. If you learn to use telekinesis to pick them up, you'll find them of much easier usage.
The early game potions, probably like the ones you use now, are pretty crappy to be fair.
Never have problems with those 2 with my Meteorb. Andy drops so fast from Fireballs that she barely manages to poison my merc (Atma FTW), and I use FO to chill Meph before Static'ing and FB'ing him into oblivion.
In low levels having a base mana is a problem. However, as you get higher up, and better gear it becomes less of a problem. My mf fb sorc has 1 pt in warmth, and a total of +17 to fire skills, giving her a lvl 18 warmth, which is more than enough. Also, as you get plus skill gear your mana costs for tele goes down. Wouldn't recommend putting more than 1 pt in warmth, you'll hate yourself when you get the really nice gear and you now have plenty mana regen and a bunch of wasted skill points.
If you're planning on playing untwinked then you might consider putting 20-50 pts in energy cause drinking all those potions can be a pain. If you can afford to be patient though, you'll have a much more powerful char at the higher level by putting the stats in vit.
I somewhat disagree. Your character won't be any more powerful with the stat points in vit than in energy. It's only slightly more survivable too (like what, you are losing out only 100 life?). Definitely stick points into energy if you are playing untwinked.