Well... a longspear doesn't really give you that much more range... after all, you could shift and attack as a move action (plus standard for the attack) rather than pulling out the spear and stowing your other items.
Besides, you pretty much have to give up your entire turn to swap weapons (stow minor kopesh, stow standard shield, minor (using your move action) to equip spear).
Personally, unless/until you can get a magic weapon that lets you use your kopesh at range (in Paragon, the Blade of the Eldritch Knight might work, as it gives you reach 5), I would simply use javellins - cheap, easy to come by, and you can stow your kopesh, draw a javellin and throw it all in one turn... or with a feet like quickdraw, you can even re-equip your kopesh.
And really, its not doing THAT much less damage than the kopesh... they both have the same proficiency and both get your strength to hit and damage (as javellins are heavy thrown), so the only real difference is d6 vs. d8 and the fact your heavy blade expertise doesn't apply (but it wouldn't for the longspear either). So the difference is really only -2 to hit and damage, as you lose out on expertise and the enchantment bonus of your kopesh... not that bad for a backup weapon. To boot, that's only -2 damage from the spear while being a whole lot more action efficient in swapping and giving you a range you a range of 20 rather than 2.
Because, face it, if a flying creature isn't going to come down into 1 square away from you, chances are its not going to spend much more time 2 squares away from you. It is, however, unlikely to have a range of more than 20, allowing you to pepper it with javellins if it does fly in to attack.
The downside is you give up the chance of a more interesting enchantment on it, but you do end up with a moderately effective ranged attack.
