5. No. Just, no. I can only imagine what IceFrog was thinking when he made that: "Hey, invis sucks for new players, so I know! I'll make an AoE invis plus speed boost item so whole teams can roflgank poor players without them noticing! And better yet, they get to blame themselves because hey, they didn't see the MIAs!"
Well map awareness is a key skill in DotA (and I'd say ARTS games in general). It's just like last hitting or positioning, if you have no map awareness, you deserve to lose; it's part of the game.
That's like playing basketball and saying: Well I can dribble, I can juke, I can pass, I can defend, I can catch rebounds, but I can't make a shot to save my life. Well that's great that you have all of those skills, but if you can never make a shot into the hoop, you're going to be kind of a burden to your team. Map awareness is just as important as any other skill, if the entire team is missing, you should know something is up, and be prepared for it.
In general, very few mechanics in DotA that purport to make comebacks actually do so, because they can easily be leveraged by the winning team to widen the gap (which people seem to miss somehow :S). Your team is ahead? Become bodyguards for your carry and get him super-farmed for a win.
Well, if you have your whole team "bodyguarding" the carry in DotA, you're actually hurting him more than helping. Gold and experiences from creep killing is the highest when you're by yourself. So if 5 people are farming a lane, they are not using their time very wisely. To have your whole team guarding your carry is actually pretty counter-productive if the enemy team is making a better use of their own resources.
However, if they DON'T guard the carry, it opens him up to be ganked, and therefore give the enemy team a chance to react. These kinds of decisions are difficult for both sides, they aren't as simple as "We're winning, guard the carry to ensure a victory!".
Use smoke of your own to stomp anyone who has the mistaken impression that they should get to play for more than 5 minutes. Etc.
Typically, Smoke is best used with a whole team, or at least most of the team, so that if you catch an enemy you can guarantee their death, then push while you have the advantage.
As I said above, if your team is already ahead, you either need to push, or continue farming in an efficient way. Pushing is much harder in DotA than in LoL, because of the inherent mobility offered by scrolls of teleport, and because towers are significantly harder to kill. So if your team continues to farm, you're not smoke ganking. Ganking when you're ahead can actually be a risky thing to do. To go onto the enemy's side of the map, close to their base and their towers, where they can all quickly respond, is a very risky thing to do. Now of course the rewards for doing this can outweigh risks, depending on the situation:
But in the situation you're describing, where you're already winning, the enemy team is already below you in terms of level and gold. You aren't gaining that much by killing them, but they gain a whole lot if the gank fails and they kill you instead.
For these reasons, the team that's losing has a lot more to gain from smoke ganks, and ganking their opponent in general. Ganking will always be the risky path to take (as opposed to farming or pushing), but it also potentially offers the highest rewards.
From watching Starcraft 2 I see similar situations where one player is behind and he knows it. In order to get ahead, or to get on even footing with his opponent, he must take a risk. He knows that if he doesn't take a risk, there's little chance that he can win. However, the winning player shouldn't take risks, they should play the game as safely and efficiently as possible, until they have a force that can simply crush their opponent. It's the same with DotA. Ganking your opponents heavily when you're ahead is an unnecessary risk, it's much more valuable for the team that's losing.
