As far as authority goes, I'd put my money with Fowler's Modern English Usage. In the first edition (1926), Fowler uses what seem to be half-spaces before colons, semicolons, question marks, and exclamation marks, but not before full stops or commas. These 'half-spaces' seem similar in length to regular spaces, or slightly narrower, but half as wide as those spaces he uses after colons etc. and full stops. The second edition (1965), edited by Gowers, look similar. The third edition (1996), by Burchfield (another authority in the field), doesn't have any space before semicolons etc.
Frankly, spaces do look a bit old fashioned to me. My advice would be to not use spaces any more; however, if you should decide to use them after all, it would still be correct—just uncommon. I believe it is still common in languages like French.
The key question here is whether a proper name whose creators included end punctuation for it must be reproduced with that end punctuation in order to be correctly spelled. If the answer to that preliminary question is yes, then we must proceed to the question that the poster asks about how to accommodate the built-in punctuation when introducing context-appropriate punctuation.
The preliminary question came up repeatedly at the consumer technology magazines where I work, thanks to the effervescent marketing personalities who graced the tech landscape with names like Yahoo!, Astound!, and Utter Bullblap!. Our arbitrary, unsympathetic response has been to treat the alphanumeric components of a proper name as integral to the name, and to treat end punctuation as promotional fluff. Goodbye exclamation points, asterisks, virgules, octothorps, and any other symbols attached to the end of a name to attract the unwary eye and sell more units of the product.
To the extent that exotic punctuation is simply a vehicle for promoting sales or market visibility, dutifully reproducing that punctuation amounts to enlisting oneself and one's publication in the promotional effort—hardly a comfortable position for an independent source of information to be in. That awkwardness helps explain why The Economist in February of 2013 adopted a no-exclamation-points-in-product-names style. I applaud that publication for its decision.
The slippery slope of deferring to the preferences of those who invent proper names, whether for commercial products or for towns and other geographical entities, is evident when you consider the annoying reverse-R favored by the Toys "R" Us toy company; does anyone not in marketing feel strongly that people writing about this company should mirror the R to match the backward proper-name style that the company copyrighted? On a more mundane level, would anyone think to include the period in the name of the restaurant chain Carl's Jr. to yield sentences like "Let's go to Carl's Jr.!" "I had lunch at Carl's Jr.." and "Do you want to go to Carl's Jr.?"? It's really quite absurd.
Best Answer
In English, it is always an error. There should be no space between a sentence and its ending punctuation, whether that's a period, a question mark, or an exclamation mark. There should also be no space before a colon, semicolon, or comma. The only ending punctuation mark that sometimes needs to be preceded by a space is a dash.
I see this error most often with people who never really learned to type. In handwriting, spacing is more, um, negotiable and subject to interpretation.