Don't ignore the early shows..operettas and musical comedies of the years 1900 to 1940 can be fun..I would suggest the following as a starter:
BABES IN TOYLAND - Decca Records made a studio cast set in the 1940s preserving 10 songs from this delightful Victor Herbert score. On CD it still sounds its age but the charm of Herbert's sprightly tunes wins the game. A later short selection recorded by Readers Digest is better sung and played by a full cast, and is reportedly available on CD and as an I-tunes download (along with similarly condensed versions of Herbert' MLLE. MODISTE and THE RED MILL. The Digest versions were long ago part of a 12-LP set (TREASURY OF GREAT OPERETTAS) featuring two dozen early musicals condensed to fill one LP side each (about 25 minutes.) The set tuns up frequently on E-Bay and if you have a turntable well worth investigating. A mix of European (DIE FLEDERMAUS, THE MERRY WIDOW, A WALTZ DREAM) and American shows (BLOSSOM TIME, THE STUDENT PRINCE, ROSE MARIE, THE DESERT SONG, THE NEW MOON, THE VAGABOND KING) even stretching the genre a bit to include PORGY AND BESS, THE CHOCOLATE SOLDIER, ROBERTA and SHOW BOAT. RD offers a CD set with 9 of these condensations. It loos as if the others will gradually be leaked out as downloads.
NO NO NANETTE - a quintessential 1920s musical comedy, and sadly never commercially recorded with the original text and orchestrations. Sony has the 1971 revival on CD and what it lacks in period atmosphere it more than makes up for in fun.
Those in search of an authentic 1920s musical comedy (as opposed to later pastiches like THE BOY FRIEND (RCA Victor) and THE DROWSY CHAPERONE (Ghostlight) would do well to check out PS Classics' KITTY'S KISSES - restored and lovingly recorded by a dedicated cast. Also see JAY's recording of GOOD NEWS - a musical about college football that is still sometimes revived. The songs by DeSylva, Brown an Henderson are delightful. M-g-M did a film version in 1947 and the soundtrack (on Rhino)makes it soudn more like a 1940's show but the songs are still great.
SHOW BOAT - a problem since each production - and recording - alter the song line-up. The 1993 Livent cast recording from Toronto (prior to Broadway) is your best bet as a single disc covering the key highlights - even if one of the main love songs (Why Do I Love You) is reassigned to the usually non-singing role of Parthy but Elaine Stritch shows a tender side singing this to the baby that surprised even her detractors. The brilliant staging by Hal Prince doesn't translate to CD but the singing - especially Lonette McKee's Julie - is sensational. For those in search of an authentic CD of SHOW BOAT as it was presented in 1927 get John McGlinn's complete recording on EMI.
1930's Broadway hits are preserved in more modern recordings: OF THEE I SING (Get the 1952 Broadway revival cast, originally on Capitol Records and most recently on CD from DRG); GIRL CRAZY (Elektra has a very complete and lively studio cast headed by Lorna Luft, David Carroll and Judy Blazer); ANYTHING GOES (John McGlinn conducts a full scale re-creation of the original 1934 version on EMI. Revivals in 1962, 1987 and 2011 interpolated other Cole Porter songs.)
PORGY AND BESS - RCA Red Seal has the complete performance of the Houston Grand Opera on a 3_CD set that is richly sung and presented with many theatrical touches. Also worth getting is the most recent revival cast on PS Classics.
JUMBO - This Rodgers and Hart classic has been pretty much ignored except for the 1962 film version. Doris Day stars on the soundtrack CD (from Collectables.)
ON YOUR TOES - An early 50's studio cast album on Columbia (On CD-R from Masterworks Broadway) is rather dull. The 1954 Broadway revival (on Decca) is much more fun and the 1983 revival (on TER) is the most complete, restoring the original 1936 orchestrations.
BABES IN ARMS - A delightful, though not terribly theatrical album headlined by Mary Martin has recently been restored to the active catalog by Masterworks Broadway. New World has an enjoyable studio cast set that uses the original text and orchestrations.
PAL JOEY - Columbia Records made the first (and still best) album of the show in 1950. It in turn inspired a Broadway revival (on Broadway Angel) and a forgettable film version with Frank Sinatra (on Capitol.) Encores Concert version on DRG stars Peter Gallagher and Patti Lupone and is the most complete version to date.
Cast albums are NOT "soundtracks."
Live theatre does not use a "soundtrack." If it did, it wouldn't be live theatre!
I host a weekly one-hour radio program featuring cast album selections as well as songs by cabaret, jazz and theatre artists. The program, FRONT ROW CENTRE is heard Sundays 9 to 10 am and also Saturdays from 8 to 9 am (eastern times) on www.proudfm.com