I have been informed that よゆう is to do with temporal or physical room, while 余地 has to do with emotional room, but I might have misunderstood the explanation.
2 Answers
From WWWJDIC's example sentences search, the results for 余裕{よゆう} mostly deal with time or money. (84 results all to do with either time or money)
彼{かれ}は自動車{じどうしゃ}を買{か}う余裕{よゆう}はない。 (He cannot afford to buy a car)
時間{じかん}の余裕{よゆう}がありますか。(Do you have much time to spare?)
The results for 余地{よち} seem to apply to a broad spectrum of other things:
彼女{かのじょ}の美{うつく}しさに関{かん}しては、疑{うたが}う余地{よち}がない。 (There is no doubt as to her beauty)(Lit: no margin for doubt)
彼の遅{おく}れは弁解{べんかい}の余地{よち}はない。(There is no excuse for his lateness)(Lit: No margin for explanation)
車{くるま}がもう1台{だい}入{い}る余地{よち}が十分{じゅうぶん}ある。(There is enough room for one more car)
(Interestingly most of the examples on WWWJDIC use 余地{よち} for "no room for doubt")
EDIT: To add on to Enno's hypothesis about 余地{よち} being more specific than 余裕{よゆう}.
Perhaps it's more about how the range of “room“ is specified rather than how specific they are.
余地{よち} starts from the outer margin and goes towards your reference point.
余裕{よゆう} starts from your reference point and goes towards the outer margin.
Of course this is just my hypothesis.
tl;dr 余地 is more specific than 余裕, and IMO the tendency Flaw observed is a secondary product of this.
余裕 can be used in the following ways. Note that I have to change the sentence a little bit if I wanted to use 余地 instead, or can't use it at all because it would sound unnatural:
Space:
タンクにはまだ余裕がある (×タンクにはまだ余地がある)
タンクにはまだかなりの量が入る余地がある
駐車スペースにはまだ余裕がある (×駐車スペースにはまだ余地がある)
駐車スペースにはまだかなりの車が入る余地がある
State of mind:
既に5点差がついているので、ゴールキーパーも余裕の表情です (×余地のある表情です)
精神的に余裕がない (×精神的に余地がない)
余裕をもって (×余地をもって)
Similarly let's try to analyze example sentences using 余地:
弁解の余地なし (×弁解の余裕なし)
疑う余地なし (×疑う余裕なし)
So there is something going on other than the difference in what the "room" can refer to.
If we compare these sentences:
まだ戦う余地がある
まだ戦う余裕がある
The former sounds more critical than the latter (i.e. the former sounds like a dismal situation. The latter sounds more optimistic). I think this comes from the fact that 余地 is more specific about how much room is left. If you say まだ戦う余地がある, you are left with just what is necessary to win the battle (i.e. you are on the edge of loosing the battle). If you say まだ戦う余裕がある, then you are not being specific and thus it implies that you still have some more room left.
Similarly, you can simply say タンクにはまだ余裕がある, but you need to specify how much room is left if you use 余地 (タンクにはまだ*かなりの量が*入る余地がある).
Similarly, 精神的に余地がない sounds unnatural but まだ頑張れる余地がある sounds ok, presumably because 頑張る implies an aim to be accomplished, which is specific. You can also say まだ頑張れる余裕がある which will again sound more optimistic.
Interestingly, 疑う余裕がある sounds unnatural probably because the brain expects that there is a specific room in the logic to be filled in order to establish a fact.
If you can create enough specificity, 余地 can also be used for money: 今年の予算に、社内旅行を入れる余地はありますかね?
So, IMO the tendency that came up in Flaw's answer is a secondary product of this.
But then of course this is just my lay-man top-of-my-head theory :p
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1+1 for attempting deeper analysis. Also would appreciate if you could provide English parsing for your examples.– Flaw ♦Commented Aug 30, 2011 at 5:12