Filero

I think you need to start with this idea of an "ideal weight". Where did you get this notion? What exactly will happen at your ideal weight that won't happen a few pounds to either side of it? I think you'll find that "ideal weight" is not a belief that you can support. If you want to get bigger, no problem, but making up some sort of "ideal weight" as justification is not required (or valid).

To answer your question about competing, obviously your natural weight at the moment is 145. You move up to 155 by adding on a load of muscle, some of which is non-contractile tissue (it doesn't improve performance) and some fat. Now, you're a natural 145er, fighting a guy who weighs 155. You'll find most guys who fight at 155 walk around naturally at 170 or more, and just cut down to 155. And in the amateurs, where you weigh in the same day, they might put 5-10 pounds back on right after the weigh-in. In short, you're fighting a guy naturally way bigger and stronger than you ... that's why fighters fight at the lowest weight they can, and move up in weight as they get older and their weight adjusts up naturally. The only disadvantage to cutting weight is if you cut so low that the cut leaves you very weak. You should not believe me on this -- I encourage you to spar some guys in your gym who are competing at 155 and walking around at 170+, and then spar a few guys who compete at near 135 and who walk around at 145ish, and then decide for yourself after you've gotten a taste.

So, if you're serious about competing, gaining weight for the sake of gaining weight, or to reach some arbitrary "ideal weight", makes no sense. But if you don't care about competing, and you just want to gain weight to look better or feel better about yourself, go for it. But I guarantee you that if you're serious, one thing you will not hear from your coach's mouth is "I worry that you're under your ideal weight, so go in the gym and get swole so you can fight guys way way bigger than you".

One last note: fighting strength and power is built in the ring, on the focus mitts, on the heavy bag, on the matts, way more than in the weight room. A good S&C program is great for a fighter, but you learn to hit hard in the ring. Tommy Hearns wasn't particularly strong, or buff, but dang if the skinny little guy couldn't knock heavyweights silly in sparring. Ringwork is your #1 asset to learn to hit hard, your strength program is an (important) supplement.