excavator701,
Generally, extending the boom and varying the element spacing can usually 'improve' a beam's gain/performance. The most common reason for that is that customers usually would rather not have an extremely long antenna (that 'extremely' is very relative), not quite as noticeable that way. Boom length and gain/performance are not directly proportional! Doubling the boom length isn't going to double the gain or performance unless the thing was a real dog to start with. In fact, it won't increase the gain much at all. It will sort of narrow the beam width a bit. Don't expect miracles.
Varying the element spacing can increase the gain/performance slightly, along with narrowing the beam width, slightly. The amount of improvement you see is going to be 'relative' to how 'bad' it was to start with (that's about like any relative, ain't it?). That 'improvement' is also going to be frequency dependent. Over about 40 channels, probably. Over a large chunk of frequencies, nope.
What would be the 'best' way to determine how long and the spacing for any particular band? Find one of the beam optimizer programs (or books) and play with it. A little 'salt' with the results of those optimizer thingys is definitely called for. Then figure the mechanical aspects of that modification. Would you think it would be worth it? Guess that just depends, doesn't it? (Just remember that a 'depends' is an adult diaper and you know what they are usually full of.) The idea is to have fun at it. If you enjoy 'messing' with antennas, then why not. If not, then not.
- 'Doc