Sell vesper Steve!

>Although they weren't really design considerations, Eo's Kontakto list and (I 
suppose) Ido's Mil Vorti come to mind. (I haven't seen the Ido list, however.) 
Among other projects, there's Loglan's list of primitive predicates and 
Interglossa's list. I have a rather odd list of my own that I'll probably publish 
online at some point.
>The problem is that some languages don't handle minimal vocabularies well. 
You need a system that handles derivation predictably, as in Eo, Ido, and (to 
a lesser extent) Occ. LFN would work too. Interlingua is a bad choice here.
Nothing prevents from making lists of basic words from languages with a full-
developped vocabulary. For example, there is "Basic English". I had compiled a 
list of 1200 sambahsa words, and posted it on Bob Petry's 
Unfortunately, he seems to have dropped the file! (but it may have not been 
up-to-date anymore). earlier today, I have already explained that every 
language tends naturally to eke out its vocabulary. Derivation and 
compounding are useful, but they cannot do everything. 

But even a list of a few hundred words is not as easy to remember alone. The 
best is to be confronted with texts (written or read) from the original 
language; then your brain unwillingly begins to locate the most used words. I 
have partly learnt German this way. And, with some experience, you can fill 
the gaps by having recourse to a dictionary. 
Another way is to make a lot of translations into the language you want to 
learn. At the beginning, it's better to start with shorter sentences, since you 
often need your dictionary! But later, you use it lesser and lesser. 

>However, it has a number of synonyms and other hallmarks of "expressivity 
and powerfulness," which was the point you were making. Also, Ia is at-sight 
readable to a lot of people (who already know a Romance language, yes), so it 
has a larger potential audience. So Ia has the advantage you ascribe to 
Sambahsa, along with an extra advantage or so, yet it lacks several of 
Sambahsa's negatives (oddball vowels, weird spelling, etc.).
What do you precisely consider "oddball" and "weird"? On the contrary to 
Interlingua, sambahsa's orthograph is fully regular since, as far as I know, 
Interlingua keeps loanwords with their original orthograph. 
Of course, an auxlang with a broader vocabulary selection than Romance will 
be less readable at first sight for speakers of Romance than Interlingua or 
Occidental. (though, thanks to its elaborated orthographic rules, Sambahsa 
generally manage to preserve the recognizability of most loanwords from West-
European languages). 
A speaker of Ido once wrote that he could understand the general meaning of 
a text in sambahsa, but not every single sentence. 

Khauris mingo quantims!