For Brutal do not reroll any dice when using a power that does not grant weapon(W) damage. If it meant to apply to damage other than weapon damage it would be worded similarly to Critical Hit.
Critical Hit DDI states:
Maximum Damage: Rather than roll damage, determine the maximum damage you can roll with your attack. This is your critical damage.
This isn't tied specifically to weapon damage.
high-crit extra x[W] bonuses should be added for any critical hit. For the powers cited there is no base weapon damage, so maximizing it has no effect. However the definition of critical still applies.
For Spidersilk Slash, you would deal 10 + 2[W] + int (for paragon).
There are three issues here, I think: Keywords, the two different kinds of proficiency, and permission by omission.
But before I go into those, a word: As always there are explicit features/feats/enchantments which break the rules, and that's why we call D&D an "exception-based" system: it deals in rules which apply universally unless (until) exceptions are made, so there is no need to enumerate the possible exceptions. We simply assume the rule unless told otherwise in a particular instance.
If a power has the
weapon keyword, and only if the power has the
weapon keyword, does a weapon enchantment (enhancement bonuses and other features) apply to that power. Ditto with the
implement keyword and implement enchantments.
Proficiency and the Proficiency Bonus
"Proficiency" means that you've had training in the use of a weapon or implement, but mechanically it means totally different things whether you're talking about a weapon or an implement.
Weapon Proficiency and the Proficiency Bonus
Proficiency with a weapon means that you can add that weapon's "proficiency bonus" to attack rolls. Only weapons have proficiency bonuses, they only apply to powers with the
weapon keyword, and they have nothing to do with whether enhancement bonuses can be applied (see below for that bit).
Implements, Enhancement Bonuses, and Permission by Omission
You need to be proficient with an implement in order to add its enhancement bonus to attacks and damage with implement powers. You do not need to be proficient with a weapon in order to add its enhancement bonus to attacks and damage with weapon powers, but you don't get its proficiency bonus to the attack roll. (In either case, you can only add the enhancement bonus of one item at a time to an attack unless you have a rules exception which says otherwise.)
I arrived at this conclusion because the magic implement rules say you need to be proficient for the enhancement bonus, but the magic weapon rules don't. Permission by omission is sloppy, but has solid precedent.
Player's Handbook pg 225
This is also part of the DDI definition of Critical Hit.