I've always wished Splunk wouldn't auto-collapse the search bar for multiline queries. This morning I dove in and figured out how to customize it.

Here's some CSS that will keep the search bar expanded up to about 5 lines (tweak the max-height settings for different amounts).

Append this to
"splunk-dir/etc/apps/search/appserver/static/application.css"
(If application.css doesn't exist already you'll need to restart splunkweb)

Tested on Splunk 4.3.2 and 5.0.1

/* keep search bar expanded to several lines for multiline queries */
.SearchBar .searchFieldWrapperInner {
    height: auto;
    max-height: 80px;
    overflow-y: scroll;
}
.SearchBar .searchFieldWrapperInner.searchFieldActive {
    max-height: none;
}
.SearchBar .searchFieldWrapper {
    height: auto;
    max-height: 88px;
    padding-bottom: 2px;
}
.SearchBar .searchFieldWrapperInner::-webkit-scrollbar {
    -webkit-appearance: none;
    width: 5px;
}
.SearchBar .searchFieldWrapperInner::-webkit-scrollbar-thumb {
    border-radius: 4px;
    background-color: rgba(0,0,0,.5);
    -webkit-box-shadow: 0 0 1px rgba(255,255,255,.5);
}