Nope not a mistake. I did envision the effects to be instant, used for 1 turn. Let's look at our old pal Dragon Lord Ken with an IQ18. If these were timed spells Old DLK could be blurred for 18 turns and reversing missiles for 18 turns for 5 EN combined. He becomes nigh invulnerable!
These instant spells are meant as disruptive spells, to protect the user for a turn, not to make a long term artificial armor protection. Also, I did away with tracking turn to turn EN use (extending spells) as it was a complication which in my experience slowed play.
If you want to create a longer lasting effect, you could create a magical item like a cloak or belt that lasts for a longer period of time...or just house rule it if you want them to be timed.
i think that it's the terminology used. when i think of instant spells i think of the effect happening at that moment on the casters turn, that's why i made reverse missle timed. perhaps, just saying 1 turn would make it not seem useless. with that mindset i'll word it 1 turn instead of instant.
Rulebook p22: "Instant Spells (I) Immediate effect or immediate single-use".
I'd change that to "Immediate effect or 1 turn duration only." to clarify, if that's your intention.
Personally, I'm returning them to timed spells as originally designed. I just don't see them as being useful as one-shot disruptions beacause this also relies on the Wizard getting to cast them before he is attacked for the spell to work. Dazzle (IQ10 EN3) is more for this sort of thing. Although Instant, its effect last for 1d6 turns.
In the example you gave of using both spells together this still costs the Wizard 5EN (which will probably only leave him 3 points) just to get through a single encounter. A similar effect can be realised by casting invisibilty for 4EN. You don't get the Reversing Missiles effect but you're harder to hit than when Blurred because you can't be seen at all.
the decision was made to make them instant in order to limit their duration. the duration = IQ turns rule is a fair, simple rule in most cases. i can understand where fenway5 was coming from. that's why i'm saying just add 1 extra point of EN cost per extra turn you want it to last...up-front, when you initially cast the spell. no book-keeping/extending. that makes sense to me.