Reprints are available from the St Bonaventure Press.

Holy Week was reformed around 1955; the Assumption Mass was replaced in 1950. St Joseph was added to the Canon in -- when: 1958? 1960?

The reprints from St Bonaventure Press are copyright 1952.

Looking around the shelves, it seems I have a 1947 edition and a 1956; I should probably sell them.

Mary, Mediatrix was not universal. Some country editions may have had the observance.

Firstly do you need an L.U. ?
1. Are you singing Sunday and feast day Masses?
2. Are you singing weekday Mass?
3. Are you going to be singing Sunday and Feast day Lauds / Vespers?
4. Are you singing daily office (Not Matins)

If only 1 you will only need a Liber brevior...
If 1 and 2 you will need a Graduale as the L.U. does not have all weekday Masses i.e. it does not have the Lenten weekday Ferial Masses.
If 1 and 3 you will need an L.U.
If 4 you really need an Antiphonale

Editions,
(more info can be found here, http://www.gregorianbooks.com/gregorian_books.html)

The L.U. printed before c. 1912, will only be useful for point 1 above and will be missing one or two Sundays, and the feasts mentioned in above posts and will not be very helpful for Palm Sunday and the Easter Vigil.

The L.U. printed from c. 1920 to 1950 will be useful for point 1, most weekdays out of Lent, and 3 (as long as you check the new rubrics and calendar changes from say the scan of the 1961 ed. on the CMAA). It will have the problems of Holy Week, it will have the new Mass of the Sacred Heart, and possibly an insert at the back for the new Mass of the Assumption.

The editions from 1955 onwards, will be the most useful if you are doing the new Holy Week etc. and Vespers / Lauds according to the 1962 calendar. N.B. some editions have missing pages and incomplete corrections to conform with the 1962.

Also there seem to be 3 types of L.U., Some have Latin Rubrics / instructions others have French or English

The advantage of the reprint of the c.1950 by St Bonaventure press is it has the Proper feasts for the U.S.A.
Also some older editions have been had inserts bound in with the new Masses for the Sacred Heart, Assumption and Joe the worker. It is worth checking the last few pages!

I have the following ed. of the L.U., 1910, 1934, 1950, 1952, 1957 and 1962. plus two Graduale from 1924.

Did Solesmes have propers for Mary, Mediatrix of All Graces

Yes, I have them in at least one book.

The reprint of the Liber Usualis you saw in the French bookstore in Rome may be the 2010 reprint of the French version of the English Mass and Vespers titled Missel Vespéral Grégorien. Here's a link to the description on Gregorian Books which includes a number of links on the right hand side to sellers who have it for under €60.

The Liber Brevior is not good for weekday Masses as it is missing proper masses for third class feasts, Ember days, the octaves of Easter and Pentecost, and ferias in Lent. Also, since it was originally published in 1954, it has the pre-1955 Holy Week, although for some that may be a feature rather than a flaw.

The LU has more of the music for weekday Masses than the LB.

We regularly celebrate Wed, Fri, and Sat (and 2nd class feast days) Sung Masses and only rarely have to turn to the G.R., but yes, the LU is not complete for that purpose. You'd have to turn to the GR much more frequently with the LB (there are many third class feasts.)

There's always the iOS app Liber Pro, as well, if you have an iOS device. Less expensive than the book, and a lot lighter too. :-)

Liber Pro also works on the iPod Touch and iPhone (just in case you thought it would only work on the iPad). It is easier to read the chants on the iPad, but it is very possible to use from an iPod or iPhone (there's a gentleman in our men's chant schola who has it on his iPhone and he uses it almost every Sunday).

The edition from St. Bonaventure Press that I saw was printed on inferior paper; the ink from the reverse side of the page showed through a bit. The old editions of the Liber were produced in some quantity, because every seminarian had one; this allowed them to master the question of the paper--opaque but thin. the reprint is thicker, but not as opaque. I would look online for a near mint copy of the old edition (probably 1955 or later).