I've been playing a gnome illusionist for years. Shadowcraft Mage isn't necessary at all. Your basic illusions are insanely awesome, with a little creativity. If you take the first racial level from Races of Stone, you get them even earlier, which, IMO, is much more potent than the make-illusions-real stuff. (No offense to anyone, since the Shadowcraft Mage is very popular: If you have to rely on making illusions real, the illusionist path isn't for you.)
Old school illusions were dropped from 4E for a very good reason: They are INSANELY GOOD. At level 1, with decent intelligence, you can already effectively cast most of the spells in the game. By level 6, you're essentially an archmage of bullhockey.
Need invisiblity for your entire group? Tell everyone to crouch down and STFU and put up a silent image of a bush. Completely legit and it only requires a cantrip.
You don't need a fireball when you can present an expected and plausible threat (and thus, no reason to disbelieve) that your opponent would naturally run away from. Something as simple as the shadow of a huge bird of prey moving across a meadow will scare off many forest denizens. (Or try a swish of a tail in tall grass and gleaming feline eyes.) A flash flood or avalanche is easy to pull off with a low level illusions and even high level threats will run before those, assuming you lead into them properly and in plausible conditions.
Think like a con artist and plan to cast as few spells every day. Every session where my gnome casts zero spells, I count as a victory, since it means I'm thinking like an illusionist and dealing with my enemies through trickery. The illusions themselves are only brought out to seal the deal. (Incidentally, pick up Bluff, Spot and any other abilities required to be the ultimate confidence man.)
You are as good of a scout as any ranger or rogue, as good at neutralizing foes as any psion, enchanter or assassin and are almost as good as a cleric for getting the party out of disasters.
You are a plan-smashing, foe-routing, day-saving badass. You are Brer Rabbit, Bugs Bunny and Loki, all wrapped up into one. If your DM ends up throwing endless constructs, plants and undead at you, it means that you've been playing your illusionist to the hilt. Go forth and kick major ass.