Learn English – What connotations does the word “semblance” have

I agree with you that this, at best, is an unusual use of the phrase "be under no illusion", while not saying that it's necessarily wrong.

The phrase implies that someone might develop, or has already developed, an illusion (a distorted view) of something. So perhaps if the conventional wisdom was "2011 is not going to be our year", the phrase "Be under no illusion, 2011 is our year" might make more sense?

This word may be uncommon enough that its connotations end up being ultimately about individual opinion. None of the dictionaries I have just checked give any mention or relevant samples to indicate any inherent connotation in the word.

That said, to me, ‘abstruse’ has a definite negative connotation, like ‘obscure’ and ‘arcane’.

Most words that mean ‘difficult to understand’ tend to have a negative connotation, simply because making oneself clear and easy to understand is generally considered a virtue (unless you’re a philosopher, in which case I imagine the connotations are probably switched), while failing to do so is considered something undesirable.

The only words I can think of in this semantic category that generally have a positive connotation are recondite and (especially) esoteric. Both these words refer to something that is difficult to understand not because it is unclear and muddy, but because it is intricate, specialised, and rarely seen—and exactly because of those qualities, it is seen as being somewhat precious.