Yes, this is how the AI often behaves. You just have to live with it. I do the following:
1. I send my scout to his base near the end of T1/start of T2. I search it during early T2. I do not bother to build hovercraft until I see that he in fact has a spaceport with which I can trade. As soon as he does, I send a hovercraft over.
2. Ignore him when he asks you to attack. He's not going to do anything significant, and it'll throw your timing off.
3. Pay attention when he asks for assistance from an attack against him. It usually means he's in deep trouble, and if you don't help him, you will soon find yourself without an ally, fighting 2-on-1 or something.
3a. I usually send some really nice units over to him to defend him before he even asks. As Naboo or the Rebs, I will send over a 3-fighter 3-bomber squadron (usually assigned #3, for some reason... I considered the "3rd cavalry" in AoK to be my "help the ally group" of horse archers and knights, and I just kept the numbering when I changed games). If I'm playing the Gungans, the Empire or the TF I will send 6 mechs over (3 of each type, MD and AM). If I am playing the wooks I will send over a few berserkers and some other troops. All depending on my own development and needs, of course.
Often I will also send over a worker, if I can spare one, which I will use to build a few extra buildings (extra air base, extra turret for defense, extra mech factory), so I can start churning out help for him really fast if he needs it. Also, if I place it right, those bases (protected by my troops and turret(s)) will draw enemy fire, taking the pressur off of him.
4. It's a good idea to tribute some excess food and wood to him if he looks like he's developing slowly, and you have it to spare. This can mean the difference between a survivable T4 ally and a dead T3 ally.
Mos Espa, Tatooine